It actually looks like they could make the web-based UI work in Mobile Safari without too much work. (Easy for me to say.) The UI renders perfectly already. As far as I can tell, playback is the only thing that doesn't work. (But if you "download" a track it'll open in the built-in quicktime player and start playing.)

Despite the Flash requirement for uploading, they're already doing non-Flash playback. I don't have Flash installed on my desktop and playback works great.

Seeing as Safari has had background audio support since before it was granted to third-party apps, the web UI would be a decent stopgap in lieu if a native iOS app.

Here's hoping it's just a bug!