Arnold Schwarzenegger is a US citizen. But Arnold will never be president (born in Austria).
Part of the interest derives from the possibility that Obama was actually born in Kenya. On other threads, people have discussed the precise wording of the law. My understanding is that if he were born in Kenya, he would not be eligle for our highest office.
Of course, other areas of interest are: Does his birth certificate list his religion as Muslim? Older birth certificates often list religion. This would not invalidate him in any way -- but it would be embarassing.
Another point (as you indicate) is that his full name might include "Mohammad". Again, this does not invalidate him -- but it would be embarassing.
I wish I were in the popcorn business.