Assuming there aren't regulatory or other barriers to entry.
The US does seem pretty bad where these things are concerned though.
In the UK we have literally hundreds of broadband suppliers to choose from. Yes the majority go through BT, but the terms etc are decided by the broadband suppliers, so you have loads of plans to choose from - capped, uncapped, cheap, expensive, etc etc
To give you an indication as of today I've used 4362MB of my 5GB cap. For which I pay $30 on top of my 512kbit/s line rental of $25). Yes, Internet sucks in South Africa.
We've got a population of +- 48 million, of which 4 million people use Internet and 1 million are using "broadband."
The high cost, low speeds, and small bandwidth allocations have hurt the growth of Internet here dramatically.
If one or only a few companies impose caps, look for rising market share of those companies that don't, probably about 1-2 billing cycles after the other companies cap downloads.
Didn't the same the happen with cell phone calls?
When is the last time you worried about "minutes"?