You're absolutely correct to say that there are sites which will be useful on a mobile device, like Wikipedia or IMDB or whatever. But the web is like one of those Ven Diagrams where there are sites that are mostly applicable to PCs, sites which are mostly applicable to mobile sites, and a large area of overlap. The area that's mobile-directed is comprised of what I was speaking of (location aware stuff, remote checkins, etc), and what defines that area is not how the information presented, but what is presented.
I guess it's basically stuff that either works best with a large detached monitor for graphics-related reasons, or stuff that requires any amount of intensive typing. I suppose there's not a huge amount of that type of thing on the web yet, but there are a few examples and probably (?) will be more in the future.
This is when most people use the mobile web:
- At home
- In school
- On public transportation