This is news to me. I've heard nothing on Google's requirements for running Android. Heck there is a youtube video of an interview at those Android classes back in June? July? Where someone was asked what will keep a carrier from tweaking the OS and they didn't mention anything about the license, just that people will want a complete system. AFAIK I thought the only license for Android was Apache Software License.
It's more the requirements of being in the OHA. The whole point is to have everything open and for the providers to mass market and sell android phones they have to agree to the rules of the OHA which basically says they can't lock anything out without showing DAMN good reason why they should be allowed. for example they'll lock out the 5.99 T-zones plan because they want people to pay for the total internet plan, that google would allow. Locking out features like using your own mp3s for ringtones and stuff like that they're not allowed to block. They can however change aspects of the device for use on the service.
For example, in your contacts theres a section called Favorites in android. for t-mobile Favorites will probably be replaced with the myfaves. And sprint will probably add all their NFL and TV stuff.
And as far as the apps store goes, t-mobile knows not to mess with that they've seen the success of the iPhone apps store and they know android will be the same way and they make money from it so they're not gonnna mess with that.
These are the reasons why Verizon and AT&T haven't joined the alliance because they don't like their phones to be totally open. AT&T might join eventually but unless Sprint and T-Mobile start kicking Verizon's ass like crazy they will never agree to the terms of the OHA.