i've also noticed that blu-rays are much heavier in the audio bitrates -- they often include one or more lossless tracks, as well as often multiple languages and/or commentary tracks
the video bitrate on hd blu-ray is usually something like 22-25 Mbps
vs about 5 Mbps for DVD
but DVD is shitty MPEG-2 and HD Blu-ray is usually H.264 or at least VC-1, both of which are much better compressors than MPEG-2
so they're better quality too - ~5:1 would be the ratio you'd expect for the pixel scale up