I think most Blu-Ray players play standard DVD's. I never was on the market for one since my PS3 has one built in, but it also plays CD's, DVD's, and other data discs for photos or whatnot, which I believe is the norm. Your DVD collection would not be lost.
I actually find Blu-Rays to be even better quality than HD cable, not to mention the audio aspects of both Blu-Ray and HD cable/satellite blow the snot out of regular DVD's or TV which have compressed audio and limited surround.