A) If Apple thought this was a good thing, they would have announced it themselves next week.
B) I would be nice if someone asked AT&T how much total bandwidth it would save them if every user used < 2GB. My guess is, not very much -- unlike home broadband, the speed throughput limit means that those 2% who use more than 2GB a month aren't using exponentially more, and are unlikely to comprise more than 5-10% of total usage. So this is mostly about charging users more (see C), than about saving their wires.
C) This is going to make Jobs's cool announcements about video chat a lot less cool. And announcements about anything else, for that matter. Stream your music and TV from the cloud! Just don't do it for more than a couple hours a day of music (you never listen to more than an hour of music on the road, do you?) or a few minutes of video a day. And please keep your chats to under 15 minutes a day -- don't want to have to pay another $10 just to see your girlfriend! And Oh, one more thing ... no, sorry, I can't tell you any more cool stuff, you're already at your cap!
Remember, every time something new catches on -- video Facebook, say? -- we use more bandwidth. 2GB might be 98% of users today, but in only a couple years, it will be 65%, or 5% if something like video Facebook were to catch on. I'm sure AT&T will then generously introduce a 5GB plan for only $39. Great price! Only $10 more than we used to pay for infinite!