In areas where something actually competitive is available, cable companies rush to improve bandwidth, or offer two-year contract deals at undercut prices to try to outlive the competition, then jack the prices back up when the competition goes bankrupt.
Some people use DSL because they're happy with DSL. DSL can be had for cheaper, and many people do not need the higher speeds of cable. HN readers and other geeks who dominate these online discussions assume that everyone is like them and that they need the fastest speed possible while sneering at any available alternative that is "just" 7 megabits. 7 megabits gets you instant page loads on any website. Sure it't not as good if you want to stream four movies to your house at once...but not everyone needs that.
The fact is that Comcast is right when they point out that they do face competition, not only from DSL but also from other services such as wireless. That you and many other people do not like these alternatives does not mean they do not exist. Many people find them to be perfectly adequate and for them the other services are the best value.
