Today, the harddrive prices today is not a issue anymore, since they got cheeper and cheeper!
Even on a 250gb, you can have about 600 Flac based albums in full quality. Flac is simply better than Wav, because they can compress aboug 45-55% without a lose of quality. Not all cd is even on 72 minuttes.
Flac but advante is, they can burn back in full quality, if one of the cd is scracted and it can not use the original anymore.
Many users do not have so many cd's, so it should not been a issue. It simply depend type of collection, and they like to preserve the full quality. You can even hear the difficent in a losebased format, when they are played used on a hi-hi sound system.