because to go forward you have to bring out a successor but everyones not going to jump and buy a new product just cos it's available. sony knew they had to price BR up and get it to be widely accepted before the benefits could be enjoyed thus bringing the price down eventually. The same happened with the PS2 and DVD - how many price cuts has the Ps3 had sio far with components getting cheaper?
This is what the 10 year plan is about - taking a year or two to get a platform built for it to thrive on, think of a relay race - the next runner starts to run before the other comes to a complete standstill then the handover takes place whilst the new runner has a little steam before it hits full pace.