Maybe it's a matter of the chipset not supporting it and not being upgradable? I don't know.
Why convert to MP3 when you have WMA Pro 24bit which seems to sound better? If it's a matter of working in Linux, that makes sense. I've converted my Lossless to WMA Pro and it sound great probably thanks to the chipset in the Zune....
My Zune 30 is not only still having a good run, but it's now grown up into a Zune 60 running for twice as long of a run..