To be honest i think the majority of the ps3 buyers will be adults to begin with. Some of my teenager friends used to be looking forward to the ps2 and xbox, but have both said the 360 and ps3 is too expensive. I also think that the fact you will need a good tv will put people off, especially those teenagers who are hoping to play offa small portable in their bedroom. Also, as you said there the ps2 has sold over 100 million units, so im expecting games to still be made for it, by 3rd party developers at least. And whilst there are still plently of new and cheap second hand games going around the average gamer wont buy a ps3 for years. And perhaps by that time most people will have huge lcd HD ready digital (blah blah blah) tv's at least in there living room anyway.
P.S I hope sony fail anyway
I would also like to point out that the xbox 360 has been out for nearly a year in the UK, yet i only know one person with one. Does anybody know how many have been sold worldwide yet?