I actually think this is less true than it used to be; the problem now is mainly on the server side. A substantial fraction of US residential customers can get IPv6 access as long as their network equipment supports it. But aside from a few prominent names -- like Google, Wikipedia, and Facebook -- the vast majority of the internet is only accessible if you have a v4 address.
From the latest statistics I could find, about 7-8% of Google visitors are connecting via IPv6 [1], but only about 1% of the Alexa top 10,000 sites are v6-enabled. [2]