Why would you trust a website asking for an email and password more?
Which has nothing to do w/ lock-in on 3rd party websites. It has to do w/ the relative security competence of those who choose to use FB Connect vs. those who choose email.
When I see a dodgy username and password form, what I parse is "I can't wait for them to email me back my password in plaintext, and then store it without a one-way hash."
That's not to say that they are the strongest professionals in the world, of course.