Comcast is one of those companies where your experience varies greatly based on which "market" of theirs that you are in. I have lived in Baltimore, MD, Pittsburgh, PA and my current location and I can tell you that services between each of the markets were drastically different. In the smaller areas they tend to not to allocate enough bandwidth for them and it causes people who should be able to get higher speeds to see poor performance and high line noise. Some of their infrastructure is just purely outdated and really needs replaced but instead they try to make it work, once again providing poor performance and poor speeds. If you are in a development that has been upgraded recently or built recently with their newer equipment you will find you get a lot better services. So, what happens is people in the old areas complain until Comcast does something, well, Comcast doesn't want to foot the bill. So their response is to hike the prices in that market to repay the money they spent to fix the infrastructure that they should have already fixed to begin with.
The other side of this is just like the VPS business they oversell their bandwidth A LOT, so when they actually do end up in an position where they are so over committed that they must upgrade, once again they pass the cost on to the customer instead of just upgrading things as they should. It isn't the customers fault that they are over committed, but they don't see it that way.
For the most part, however, in my recent location that was built with-in the past 10-15 years the infrastructure has been built up correctly and I actually get the best performance now from Comcast than I ever did in the previous markets I was in. Before in Maryland for example I was limited to 20/1 and now where i am with the same service I get 70/10.
However, I do rent equipment and I firmly believe the amount you agree to pay going in for that should be the price it stays, its kinda bogus they can randomly change that on you.
Cheers!