I am constantly logged on to Quora so haven't seen the login form for ages, but I don't remember it was Facebook login only. I have a regular old school login there. I certainly don't link or join anything that forces me to link my Facebook account to it.
It is not facebook only. I don't use facebook. I don't remember now, but I may have logged in with Twitter authentication.
And you're too busy to verify that so this is just speculation?
You're right, you can definitely login without a facebook/twitter account now.