Well, DVD and Bluray are different - different wavelength laser, different numerical aperture and different focus depth. They could get rid of the red laser to save a few bucks …
Software wise, the data structure is different between DVD and Bluray - MPEG-2 is common, but AVC and VC-1 isn’t. Neither is BD-J.
A bluray player is quite a lot more demanding in terms of processing power. Because the processing power is there, only software has to be written to take support for DVD. Likely - as it is now - red lasers are in such high rates of production that it would only be a few dollars more to add a red laser on - and tweak the firmware to support it. It would currently be “unwise” in terms of the market to release a bluray-only player. In the future it might be possible, but then again, as I said - it would be fairly easy to make it backwards compatible … so I don’t see why they wouldn’t.
Just as a side note - you’ll see most DVD players can play CD’s - it is only a little software support and tweaking that they have to do to make it happen. Likewise, most modern CD/DVD players actually have two lasers as well. Earlier DVD players used one laser to try and read both CD and DVD but the problem was that the DVD laser wasn’t reflecting well off the burnt discs causing poor readback - it was initially a technical and cost saving measure - but things got so cheap that even a very lowly DVD player has two lasers in it. Not even the cheapest DVD player that I can buy won’t have CD support.
It’s always nice to put a few more words on the box when you’re trying to sell something. So if my crystal ball says correctly - backwards compatibility to CD should be around for as long as we evolve storage media which are all 12cm in diameter with the same hole in the middle, with the same sort of thickness.