3 Reasons Why Facebook Connect Will Be Our Only Sign-in Option For Now

Makes total sense. Using registration/authentication as a deliberate strategy for selecting/segmenting your market is underrated.

Startups too often get in a cycle of wanting ALL the customers, instead of wanting the right customers.

You're not walmart, you're not trying to please everyone. Time is at a premium, so if your userbase is mostly on facebook (and willing to authenticate via facebook), don't waste time supporting everything under the sun.

Wait until 1000s of people say "Hey i'd like to be able to auth via X" before you build it.