Some points I want to talk about, and mainly, have to agree with Bernard
-What is DX? I remember it from the film, it was the ability of the camera to decode the ISO value of the roll.
-I have to fully agree with Bernard again, and shout: ARE WE MENTAL ABOUT THE SIZE? If it is about impressing the client, then I could agree somehow about the size factor as a WOW factor. But we still have to remember that almost any of the point and shoot currently available with decent performance will put to shame high end machines marketed five-six years ago. Pushed enough, any system will be able to produce good enough images. If you have to hike and travel as light as possible, the smaller the equipment the better.
-That being said, I think that Olympus, Pentax and Sony are trying to play a different approach to the war Nikon and Canon are having. Which is fine, and smart at the same time [coming back to this later on].
-The lens issue. A nominal 300mm lens is a 600 lens in full format, and a 400 in APS-C sensors. That means that the lens is way smaller than what a APS-C owner or a Full Frame owner has to carry around. Because, to be honest, if you were to use those long lenses, you would either hike for birding-landscape photography, or do sports photography. Two activities where size does matter, and the bigger the lens, the more of a hindrance it becomes.
-The lens approach of each brand is quite different. And personally, I find Canikon lens catalogue to be too big and too messy. You will find the very same specs for the very same focal with different qualities and separated by some hundred of euros/dollars. Still, if you go for the expensive one, you will find that you only gain half a stop of exposure, but the quality of the lens is not as good as the cheaper version. That happens quite a bit with Nikon, specially if one is trying to build up a system composed of a FF body and a APS-C back-up. You will find that the lens which performs brilliantly on the FF body does not a good job with the APS-C body, and the other way around. That is most definitely not a good way to get a good system, and if fidgeting up close, will make you buy a double system. Not good.
-Regardless the size of the companies [where only Sony is comparable to Canikon], and as stated by other people before, the sales are driven by shelf space AND something called market inertia. If you do not get enough shelf space in big stores where most of the market share is decided [FNAC, WallMart, BestBuy, and so on], then forget about making it big. Pentax and Olympus lost that war precisely when those big box retailers started to gain momentum. Therefore, they are starting to differentiate themselves with size and price. Specializing in small bodies [Olympus] and small lenses [Pentax].
All in all, I [for the third time] will have to agree with Bernard and not only make compulsory to buy a 4/3 body periodically, but buy a pancake lens or the smalles t lens available for the needed focal length.