That's right, practical solutions are always the best suited alternative. The thought of being entirely independent is a tempting one, it's definitely a very cool idea, however it's not always the best thing to target.
OCRemix is very successful as it is now, and for what i can see there is no problem in using mp3 format... i think. Or... have you ever had some kind of limitation?
Anyway, i thought maybe ogg would be a solution to overcome any possible limitation with mp3, but it seems there's no such a barrier and moreover, the change would perhaps be a practically bad move.
Besides, i guess if at some point the limit existed, you guys would already had evaluated the possibility to change.