Backwards compatibility is a major feature for some buyers. Heck, I own more GC games than Wii games, and I never owned a GC. Dropping BC may have helped them drop the price, but it's also dropped the value of that SKU.
Perhaps Joe Blow might not care about BC, and gleefully buy a cheaper PS3 without it, but I can also see Joe Blow assuming that his cheap PS3 can play PS2 games. After all, PS3 had great BC at release, right? When he picks up a couple PS2 classics and finds they won't work in his $400 PS3, Joe Blow might be righteously cheesed off.
"The worst part about these reviews is they are [subjective]--and their scores often depend on how drunk you got the media at a Street Fighter event." — Mona Hamilton, Capcom Senior VP of Marketing
*Image indefinitely borrowed from BrainBoxLtd without his consent.