Why do people rip using iso/mp3

I think the rip depends on the machine:

128k mp3 seems to sound fine on a SegaCD... I can't hear any artifacts or anything. Maybe the D/A converter in the SCD isn't that great.

Saturn on the other hand, I think 160k or higher is best. At 192k I can't really tell the difference between the source material and the mp3.

I also really hate wma and realmedia, and mp3pro doesn't decode right on any non-mp3pro decoder (it decodes at 22kHz).