Comcast sucks at everything they do.
I have had quite the opposite experience, to be honest. I had RCN for a while for internet/cable/phone and my mom switched to Comcast after RCN were being douchebags about billing or something, and we're now paying less money and getting better service (at least internet-wise, the other two are pretty much exactly the same), as well as having much easier to deal with customer service. They've been especially nice about offering free upgrades and stuff now that they are competing with the verizon fios thing.