The whoel notion of backwards compatability can REALLY help to push the sales of a console. A lot of people resisted PS2 until they found out they could play PS1 games on it. Then PS1 doesn't seem like such a waste of money.
Also, this is america and people want free shit....even if it's shit they don't need. If you make someone feel like they got a deal (ie packaging a game or two with the console) then they'l buy it. When people go to Walmart or Target, they go there needing dishwasher detergent. They come out with $90 worth of shit. Why? Because they go "Look honey!! This ceramic cat is only $3." "We don't need a ceramic cat." "I know, but it's only $3. $3!!!!"