To be honest, I believe the problem lies that US carriers don't know what to think about the OTA updates. The moment US carriers start charging tiered plans, and this update is big---its not just Froyo update, it is also a Touchwiz update---who is going to pay for the 100mb of so of download through the wireless? The bill gets bigger when the carriers want to include some of their bloatware with it.
Basically, the bigger the update, the more you have to figure out who is going to pay for the costs of data moving them all into your phone. The consumer, the carrier?
So the answer lies using a PC sync program where all the data is moved using the wired internet. Basically no different from the iTunes/iPhone combination. Actually, no different from any other, since Symbian, Blackbery and Windows Phone all use some PC software to sync and update the phone. Only Android and Palm WebOS is adventurous to do the entirely on the air thing. Nokia used to have updates pushed entirely on the air (see downloads folder), but they have gone to using their PC Ovi Suite software instead of late.
Sony Ericsson pushes minor updates on the air, but big updates, like Android 2.1 update for the X10, is done with PC software.