The new set up uses a third of the power of the old one, the cpu is smaller and slimmer requiring less juice and cooling, so it should be more reliable than the older version too. You won't notice any difference between the 2 except the newer version will load faster due to the faster speed the HD can work at and because it needs less cooling the fan is even less obtrusive then the already quiet "old" ps3.
As for exclusives, off the top of my head.
warhawk
Uncharted
Rachett and clank
Final Fantasy
Gran Tourismo
Originally, most games were ported over from the Xbox to the PS3 and it showed, software houses are now getting to grips with the hardware and more and more games are now coded specifically. As an added bonus the bluray's massive capacity means that it can hold much, much larger games than the Xbox's disc, Uncharted 2 could not have been released on a single disc for the Xbox (but's it's ps3 only).
At the end of the day, get the console that most of your son's mates have so he can play on-line against them, if you want something to use as an impressive media centre/bluray player then get the ps3, oh – rememebr to get a HDMI cable too if getting the ps3, but get a cheap one, because they are all the same quality.