I'm sure most HD people will have one BRD player by then, but how many of us have more than one DVD playing device that's used? Lots of people! DVD/BRD players, laptios, consoles, portable players. One is never enough! As I say, it's added value. If a BRD player costs $100, then having that in your console is a $100 feature, as it were. If you're going to have an Hd optical format, it's almost certain to be BRD, and if it is, then you may as well provide BRD playback for minimal effort.
A $100 feature is never $100 value overall when bundled with a system which does other things. On average it has to be less than that because otherwise Sony would have completely blitzed Microsoft with their $400 then $300 then $200 etc value Blu Ray drive.