What counts is the size and weight of the whole functioning camera, including a lens, and of the whole kit including any extra lenses.
I suppose you know already I can't let you get away with these illogicalities and non sequiturs .
What counts for many of us (perhaps most of us passionate about photography) is functionality, ease of use, and high image quality. Size and weight is of secondary concern unless the size and weight difference is very substantial and taxes our muscles and causes us to get exhausted. Since I'm not suffering from muscular dystrophy or any similar disease, I'm prepared to carry a bit of extra weight for the sake of better image quality.
But this is my personal view, which is however backed up by my own behaviour with cameras. I own a range of cameras from a tiny 5mp Sony T1 which literally fits into a shirt pocket, to a very heavy Mamiya RB67 nicknamed 'the tank'.
I no longer use film cameras for reasons of their limited functionality and ease of use. Weight is not a major consideration. Of the 4 digital cameras I own, by far the lightest, the T1, is the one I have least used. The next lightest combination of body and lens would be the 20D with EF-S 10-22mm lens. Do I use this in preference to my 5D with Sigma 15-30mm lens? No I don't. A clear advantage in image quality plus slightly greater functionality (bigger LCD screen, for example) means more to me than a weight saving of a few ounces.
Smaller formats and their higher resolution (more l/mm from smaller photo-sites and the fundamental optical advantages of downsizing lens designs to shorter focal lengths and smaller image circles) allow the user of smaller, lighter lenses, particularly for telephoto.
Same counterpoint as above applies. If the lighter lens does not also provide equal image quality, including equally low noise, there's no over all advantage for me.
So why do you keep looking at body weight only?
I clearly haven't. I specifically compared the weight of two lenses of equal focal length and equal maximum aperture, designed for different formats.
The current trend is for pixel size ratio between formats to hold steady or increase, not decrease, so if anything the focal length differences (as ratios) needed for equal resolution after cropping are increasing not decreasing.
Non of us have crystal balls in these matters. As I recall, the first 8mp cameras were P&S, followed by the DSLRs such as the 20D. The next generation of Canon 1 series cameras is likely to be 22mp, but who knows. Whatever technology goes into the small format cameras, is likely to be applicable to the larger format, thus maintaining the quality gap.
And since this is a thread about the 16x24mm format Pentax DSLR's, why do you persist in doing so many of your price/performance comparisons based on 4/3 and the Olympus 300/2.8? Why not compare to either Pentax lenses, or to Canon FF's most direct competitor, the Nikon DX system? Try Nikon 200/2 or 300/2.8 vs Canon 300/2.8, or 400/2.8 or 600/4 vs Canon 600/4.
I was responding to your comment in your previous post, ie..... "To go from 4/3 with my 50-200/3.5-4.5 to 35mm would require a heavier lens: 300-400mm, and faster than f/5.6 to match AF performance, so distinctly heavier (AF speed depends on a lens's minimum f-stop, regardless of format or focal length. That is why f/5.6 is the slowest for almost al lenses, in any SLR format.)"....
I use the example of the Zuiko 300/2.8 rather than the Nikkor 300/2.8 because I don't believe there's a Nikkor DX 300mm lens. Having checked on the net, the Nikkor 300/2.8 is slightly heavier than the Canon, probably of no better quality than the Canon EF 300/2.8 and, since Nikon doesn't have an FF body, what's the point of such a comparison.
The bottom line is, the smaller format cameras such as the 4/3rds, and the high pixel count cropped format cameras such as the Nikon D2X, have sacrificed noise performance for the sake of extra resolution (lp/mm). The D30 has lower noise at ISO 1600 than the D2X. The smaller format cameras are forced into this position in order to maintain an edge, but ultimately the only edge they have is a modest reduction in size and weight offset by an inherent image quality advantage of the larger FF 35mm format.
If you wish to make the argument that most people will sacrifice image quality for a modest reduction in weight, then that's a fair comment and probably true. What I'm suggesting is that most people who are passionate about photography, the sort of people who read this forum, will not sacrifice quality for a modest or slight reduction in weight if the price is right.
But for one thing, surely MF SLR's also offered through the lens focusing and interchangeable lenses, and the better established MF makers should have been equally capable of adding those SLR style features if their products were in other ways more desirable.
Here I'm addressing your previous comment, ..."I was thinking particularly of the transition period, roughly the 1960's. People who a decade earlier were buying and carrying MF gear instead chose the smaller 35mm "miniature" format. Yes, size and weight is probably a major factor"......
The first camera that I was really excited about was the Pentax Spotmatic which I bought in the early 60's. A friend bought a Rolleiflex twin lens reflex with Planar 80mm f2.8 lens about the same time. We used to go out shooting together. As I recall, his camera had a fixed lens and no through-the-lens metering. I used my camera much more frequently. I had a 50mm and 135mm lens, the advantage of rolls of 36 exposures and basically what I would describe as greater functionality and ease of use. There's no doubt that the 6x6 Rolliflex produced better quality images, but the penalty was not only greater weight and greater expenses, but more awkwardness of use, greater continuing expense of film and processing, lack of interchangeables lenses and so on. I believe it was quite common in those days for MF cameras to lack many of the features of the then modern 35mm camera. This is not the case whaen comparing cropped format DSLRs with FF DSLRs. That's the point i'm making.
(My guess: you compare so often to the Olympus 300/2.8 because it is a very expensive, highly specialized, rarely used, special order item that allows you to make an extremely unfavorable but also extremely atypical comparison to the far more widely used and better selling 300/2.8 lenses for 35mm format.)
By the way, the last time I visited my local camera store in Brisbane, I saw this Zuiko 300mm lens sitting behind a glass case. It was in stock and on display. No special order required. I would say that generally I'm interested in photographic gear if it can do something for me that I can't already do and provided it's affordable. If this lens was less expensive, then the promise of equivalent 600mm performance on 35mm would be a reason to buy into the 4/3rds system. However, I doubt that one would ever achieve the image quality of a 1Ds2, or even a 5D coupled to a 600/f4, although there is no denying that the 600/4 is a heavier lens, but not necessarily much more expensive.