Why can't you create an account for answers without having a Facebook account?

Of course I can't answer for (no pun intended)Answers.com. However - the logic with sites using only Facebook 'sign-ups' and 'sign-ins' is more about gathering relevant marketing information from someone's Facebook profile more than simply using the feature.

For sign-up(in) to work, an APP must be developed which usually gathers data for future marketing opportunities. Truthfully - this is actually much smarter than developing a brand specific sign-in feature.

It allows access to millions of people which answers (and any other site for that matter) could never access for marketing purposes using brand specific methods. If they did decide to 'go it alone' surely to access the same amount of people would take years and hundreds of millions of $$$.