PS2 BC was scrapped because people don't play PS2 titles anymore. They weren't going to keep putting an EE + RS chip in there just because some 0,05% of the PS3 customers want to play Final Fantasy X, even though many of them still keep a functional PS2 unit.
BC that requires dedicated hardware made sense during the initial stages of the console, where the added portfolio came as a true advantage. The PS3 now has a very large game line-up with many great titles as it is. BC compatibility with ~10 year titles isn't that important anymore.
While i agree with your post sony removed bc because ee+gs cost them sth like 20-30$ per unit iirc and not because lack of costumers interest for bc.