Boy do I think this is a mistake by AT&T. Yep, 3% of your users take 40% of your bandwidth. Those 3% are the ones who use your phone to the fullest. They show it off. They post on blogs and forums. They sell your devices for you-- for free. They are doing all the things with it you told them they could when they bought it. Nope-most users won't broadcast live on Ustream, listen to Pandora all day, use augmented reality apps, or watch HD programming. The ones who do though will show it off a ton and sell more devices for you. Go ahead and charge them more-- as long as other carriers don't follow suit, you will lose customers to Android, WebOS, BB, and WinMo.
Charging customers more because you want to discourage them from using the network you built that cannot support the devices you put on it and sold them is just bad business.