From the train of thought on the side of the tracks TJ doesn't walk on....
Some people buy the new system to replace the old system, not buy a new system to sit beside the old one.
When you bought a Bluray player, you probably didn't leave the DVD player hooked up too. I'm sure you disconnected it and put it in a box (or moved it to some other room you don't frequent often for movie viewing pleasure). I'm also sure you expected the DVD's you already purchased to work in your new Bluray player since it also accepts disc based media and claims to play movies.
Doesn't seem too far fetched to expect the new system, in this day and age, that accepts the same Bluray disc media, to play the old Bluray Disc media too. Seems very logical to me actually.