Hi,
The main reason why it's not recording in WAV (or AIFF) format, is the file size (uncompressed format)...
Moreover, most of the users won't really see the difference between the current m4a recording and a potential wav recording, especially if played thru crap Apple headphones on a crap iPhone
It might be added anyway in the future, but a better solution would probably either to increase the m4a quality (user defined or not) or to add the possibility to record in some lossless compressed formats (either ALAC, if possible, or FLAC).
Cheers,