I know this post is kind of old, but I just saw it now...
I didn't realize there still wasn't an update in the US for Galaxy S. I had mine patched to Froyo last summer so I haven't really cared about carrier upgrades. That phone is a real shame. For such a nice piece of hardware, the software has something to be desired even for the non NA ones. The lag problem was never properly addressed so you have to run a hacked ROM if want to eliminate it. I really don't know why Samsung refuses to get rid of the rds file system that causes it.
I think part of the reason the NA carries might be reluctant to pay for the upgrade is that there are many problems that are still not fixed in the phone. I recently switched to a Nexus S and I can tell you so far the only downside I see is that it doesn't have an SD card slot. Gone are the GPS, lag and other issues.
The other thing is that all the phone makers seem to think they have to create "special" versions of Android. They can't just tweak the setup and drivers for the hardware, they seem to want to try to add their own features etc. Stupid, stupid, stupid. Look at the PC market. No one bothers to try to "hot rod" the included OS anymore. They used to, but it had more problems than gains. They need to start following this model, but I suspect the carriers are opposed as it is "uncharted" territory.
It will be interesting to see where this goes over the next couple of years. My guess is it will be the same as the PC world. They will have more updates, but fewer custom features. The manufacturers will concentrate on making good hardware etc and leave the software to Google.