I've had this happen a couple times now where all my Satellite radio presets will be erased but the FM presets will still be retained. I always use the same key so i don't think its tied to the key memory. I know when I used to have a external Sirius Radio unit that every couple months there would be a channel update to download. Maybe its related. Anyone else seen this anomaly?

 

I lost mine a couple of times after I asked the computer to reset the tripmeter. I figured it got a little carried away resetting. I don't know about the fm presets as I don't have any only the satellite ones.
I since only reset my tripmeter with the button in front of the steering wheel.
Mine also just powered down my radio once and when it came back about 5 seconds later the presets were gone.
So you're not alone, but I have no solution for you. Mine hasn't done it in a while though.