Why Digital Download Games aren't Mainstream yet

What do the Xbox 360 and PlayStation 3 have in common? Yes you can play videogames, but it's the ways in which you purchase your games which the question is implying. What options does a consumer have when buying their games? Can consumers only purchase in-store, or can they purchase online? One thing that was introduced in this round of consoles is the ability to download a game straight to your console without having to go outside your house, or wait for a shipment to arrive.