Not for lack of trying. I recently helped my friend set up Comcast and part of the installation process included downloading a required suite of "configuration" software. We were able to figure out a way around it but most people probably just click through without a thought.
The worst part is that it only keeps me in the captive portal just short enough that I haven't been compelled to figure out how to make dd-wrt stop it yet. I'll be sitting there putzing around on the Internet, try to google something and hit their portal. A few refreshes later and I'll be back in business.
However, they only have Windows and Mac versions of the stuff.
That or I could just have logged into my freebsd router off the serial port and said have at it, good luck, but that would be mean to the tech.