If you create an account immediately after asking a question, that question can be assigned to your new username instead.
Publishing the IP address in the page history of a wiki is a standard feature of the MediaWiki software that Wikia (and Wikipedia) uses. This is the simplest way of identifying a user who has not logged in.
Wikianswers usually displays the nickname of the asker. In cases we don't know their name, we show their IP address in the page history and the phrase "A Wikia user" on the question page itself.
The advantage of knowing a user's IP address is that you can see what other edits they have made, and you can block edits from a certain IP address if an unregistered user is causing problems such as vandalism or spam.