As noted, as new games still come out for the PS2, then Sony don't need to give the PS3 the compatability -- that was pretty much hit-and-miss anyway !
Most folks have the PS2 anyway and if not and you are a new PS3 purchaser then you're not going to be impressed at going backwards to PS2 games so unlikely to buy any of those.
It makes sense for Sony I think...... Entry level gaming is available on the PS2 and then when you want to "upgrade" you buy the PS3 and instead of the PS2 being sold for £10 or dumped in a cupboard somewhere you can hang on to it for those games
"A woman without curves is like a road without bends, you might get to your destination quicker but the ride is boring as hell'