They all will play DVD as well as CD, and most do it quite well.
A lot of the cheaper "no-name" players will also play VCD, CD+G, MP3 CD, and some will play a DVD full of MP3's, as will a few DVD players.
The reasons I got a Blu-Ray player?
1. It was super cheap.
2. It has 3D, although my current TV doesn't support it, the next one will.
3. It does Netflix, Vudu, and YouTube.
3. It allows me to rent a Blu-ray @ Redbox for just 30 cents more. (very handy if the DVD version is out of stock!)