VGChartz is full of hardcore gamers (including me !) for which BC is important (being able to play some oldies is great)
but for the average customers, what is the interest to play Madden/PES2006 when the 2008 edition is here.
Same for GTA or Virtua Fighter or GT.
Even if hardcore player would like to be able to play MGS1/2/3/4 in the same console, the casual gamers, IF he is interested in MGS4, will just buy MGS4 !
Same for Halo3 for example.
For us, BC is important.
But for the sales, BC is not important and absolutely not critical.
This is why Sony dropped it.
On the contrary, I'd speculate differently...
Most "new" gamers won't start gaming with a hugely expensive beast like the PS3. I can imagine it would be quite hard for a 12 year-old to convince mommy and daddy to drop $400~$600 on a toy.
Most "average" gamers this generation likely started their gaming experience with the PS or PS2. Not being able to play their old games on the PS3 is probably pretty important to them because those represent the gaming world to them.