I am bringing an old thread back for a few points:
1. Comcast is not the only provider to do this, my ISP OOL is normally not strict at all, except when it comes to abusing upload. Upload at 128 KB/sec for a few hours and you get capped down to 28 KB/sec upload.
2. They are within their right to do this, it is stated in the TOS/AUP. No arguing about it, people know about it when they sign up.
3. Speakeasy while cool, is also very expensive, that is why they don't need to care about how much transfer you do, as at $130 which was quoted to me, it covers almost all the transfer you can do.
4. After about 100 GB of transfer, most cable companies that provide internet are not making any money anymore. 200 GB is when they are about even when it comes to money, at 300 GB and above they are losing money on a customer. (Stats from an OOL employee I know, at $50 for 10 Mbit down, 1 Mbit up).