There are several possibilities:
1.) Since there are only so many possible (normal) facial structures, and billions of people have lived and died, it's not hard to believe that similar faces turn up quite often.
2.) All famous people are actually vampires who have been alive for hundreds of years, and they got famous because they have had so long to practice socializing and generally living life so they basically know how to cheat the system.
3.) It's 3:00 am and I need to go the **** to sleep.
I do believe there are aproximately 1 bil different facial combinations (excluding colors, such as skin, hair, eyes) simply based on structure. So there are 7 of you at any given time right now, of various ages and races.