Sorta true... There's actually a *huge* difference in video bandwidth and quality as well... The short answer is DVD's are standard def, Blu-Ray is HD. There's all sorts of upscaling/bs about what is really true but this is a first approximation.

VIDEO
DVDs run effectively at 480p, Blu-Ray disks support 1080p. That's roughly 4x the pixels, and the data rate is roughly 4x as high. On top of more data, the video compression techniques for DVD are all MPEG2, while Blu-Ray supports improved AVC and VC-1 codecs... This all means terrific video quality, but it requires a High Def television to take seriously.

AUDIO
As Pug said, again lots more data for multi-track audio, very high resolution. If you're playing the sound out of your TV's built in speakers, probably not a big deal. If you are a home theater geek, you'll appreciate it.
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