My thesis is not that people reject OpenID for that reason, it's that OpenID exists as an ethereal add-on to other services. That is to say: it does not exist in and of itself. Facebook Connect is an extension of my Facebook identity. Twitter Connect is an extension of my Twitter identity. OpenID is NOT simply an extension of the listed providers in the same manner.

I'll illustrate the point as such: My username is Sayter. 1) Go find my Facebook. 2) Then go find my Twitter. 3) Now go find my OpenID. You immediately know where to go for the first two, and in fact can type in the url's for my Facebook and Twitter accounts directly. But how about my OpenID? Is it my Gmail? Yahoo account? Windows Live account? All of the above? Whichever I use the most? Or is it the OpenID that I have on one my domains? My identity for OpenID is fragmented (I'm not even sure how many I have, honestly) and does not exist in a single space, while Facebook and Twitter do exist in single spaces (assuming I only have one Facebook/Twitter of course, but that possibility was simplified for the sake of argument).

That is a non-trivial problem that Facebook and Twitter have (mostly) solved, while OpenID is still struggling with it.