Hey Rob,
While digital images don't organically create that type of grain, it can be reproduced digitally (we can argue quality later). To my knowledge there are two ways to create the type of grain present in film. You can recreate from scratch digitally (generating noise/grain etc in PS) or sample grain from existing film images. While there isn't a huge database of different types of grain available from different film stock, I think it's a matter of time that either of the aforementioned solutions bridge the gap between digital and film effects.
Is digital reproduction of film grain there yet? No. But you can't stop evolution. You're absolutely right about the size of the image and the size of the grain having a nice relationship that makes for a pleasing effect. On the other hand, IMHO it's irresponsible for as photographers to relegate grain effects strictly to film
we should keep pushing for ways to develop whatever effects we seek in digital.
On the other hand, there are people who don't want to push ahead. People who think digital photography is a fad just like the Internet is a fad. People who are afraid of Photoshop and don't like retouching. Hell, there are still people that think retouching is "cheating".
But there's no right answer. Different strokes for different folks. And I sure as hell don't have all the answers. That said, I for one am still seeking ways to reproduce grain better than the current methods I use now. I absorb and digest as much knowledge regarding post-processing as possible.
Here's another image. I didn't try to replicate any particular film stock or anything so I'm sure it falls short of traditional grain effects. I simply applied several techniques to generate grain in this look. It's sharper than most of the older film images but that's because I like my images sharper:
Cheers
Charles Lucima