[H] Blu-ray DVDs

[Winterlight]

Ok, now that I have a HD TV and blu-ray player on the way, I started 
looking at blu-ray DVDs which, surprisingly,  are now priced not much 
differently then regular DVDs.... but they hold 10 to 20 times the 
data...correct?

You can download a SD DVD no problem, and typically SD downloads have 
been re-incoded into something more mobile like mkv or mp4 with 
little or no loss in quality. But that can't be true with blu-ray can 
it? A ripped blu-ray must be 50 to 100GB ... right? How is the 
quality if  ripped to download, or put on a media box. Can it be done 
in such a way to retain the original blu-ray quality? How does this work?

thanks
w