Well I don't know what an .ogg is, but the difference between a lossless file and even a 256kbps mp3 is quite obvious to me on my system. And I'm not bragging about my system, it's not <i>that</i> great. (well okay, my Transparent speaker cables are friggin' awesome, probably better than anyone here's except maybe Gilmour's, but only because I got them for 70% off when I worked in a hi-fi store for a summer)
umm, see kjl's posts. Actually much of what goes over the internet is losslessly compressed, especially text. If the html file your browser requests gets corrupted en route even by one <i>bit</i>, your file has to be re-sent.
CDs get scratched, fingerprinted, lost, stolen, bitten, etc., especially by four year old boys named Teddy, and one year old girls name Dory. Also, you can't play a shuffle of your <i>entire collection</i> in your CD player (assuming it's not a jukebox).