In the US, cable companies are often monopolies in providing broadband internet. They get away with offering mediocre product and poor service simply because there are no alternatives.

I've had the backwards situation where it was cheaper to buy basic cable TV + cable internet than stand alone cable internet.

It would be foolish of them to offer a cheaper, limited cable internet plan when they can make everybody pay more for their standard, unlimited (that is not unlimited) plan.

From my small town of 10,000 people, to my college town with 100,000, to my current home in San Francisco, there has always been at least two broadband providers: usually the local cable company and AT&T DSL. Perhaps this isn't the norm, or perhaps two companies with completely separate local infrastructures isn't enough competition.

DSL is not good competition for any reasonable cable internet service. In Pittsburgh Comcast's $60 a month service is 5 times the speed of the $25 a month 1-3 mbps DSL service offered by Verizon DSL. The DSL connection is barely enough for reasonable quality video streaming, but it's not enough if you want to have two people use pipe at the same time. FIOS does provide decent competition but it's availability is limited.

You can get two lines and bond them.

That's about as useful as taking two slices of bread, gluing them together, and declaring the result a complete bakery. You'd have to get ten bonded DSL lines to compare with the speed of a cable modem in my area.

I'm not sure if whichsituation is "the norm", but my area (southwest Georgia) and many surrounding communities only have one cable choice. In some of them there is a public option as well, but not many.

This is substantially what AT&T has done for the iPhone data plans.

200MB - $15/month 2GB - $25/month

Albeit without the higher speeds.