Once you've recorded to one of those formats, you can always convert it to MP3.
I'd recommend using Audacity and the LAME encoder since it's Cross platform (windows/Mac/Linux) and free.
Just load the wave file, and then export to the bitrate you want the MP3 in.
FYI - One likely reason for this is that converting to MP3 requires purchasing a license for the Fraunhofer algorithm - which can be quite expensive. LAME isn't legal for distribution in all countries and while it creates MP3 compatible files, it's NOT an MP3 encoder (LAME actually stands for, "LAME Ain't an MP3 Encoder"). I find the quality actually BETTER with LAME over Fraunhofer at the same bitrates....
But that's all technical stuff you probably didn't need to know but I find it cool anyway.
c00l People MV Society 
