mp3's have different encoding system..like LAME...iTunes (fraunhofer)...etc...if it falls below 128kbps then that's i consider low quality...i am currently contented with the 192kbps or VBR...but nevertheless audio cds from music stores still sounds different..if i have disposable income i would prefer the cd's in music stores...one would know if your using nice audiophile gears...
but..iPods just make it more convinient..way more convinient...blame it on technology...