Most 720p rips I see are around 4GB. Wouldn’t trust a 1080p rip under 10GB myself, and as I don’t have that kind of bandwidth to throw around on a regular basis I usually stick with 720p.
As for Blu-Rays, a lot of them use MPEG-2 (like DVD/SVCD) rather than MPEG-4. Lower CPU overhead, power consumption, and heat output. And it’s not like you’re gonna be using the space on the disc for anything else; if it fits why not use it? Course not everything does fit which is why other films use more intensive MPEG-4-derived codecs.