Advertising. Market penetration. Most consumers don't do research when they purchase things. Impulse buying. There are many reasons why people pay more money for things when there are cheaper and sometimes better alternatives. I'll just leave it at ignorance of the masses.
This is too new a technology. If you're first to get facetime you get the mindshare and everything else will seem inferior (especially if you have a good store display like the one on the picture). As ChiefScooter said, most consumers do not do adequate research before buying. It's a brilliant marketing move.