Numbers like that sounds of something fishy to me. So far I haven't seen numbers like that in my district that I'm aware of. The highest amount I have seen is 110% at my store.... the location I work at is usually pretty slow, at least around the Electronics department, most people don't want to add on item's, some days get lucky, some don't... I can see those numbers during the Holiday's though, especially around Black Friday.. like I said, to me that sounds like a Red Flag if stores are getting that much of an attachment rate. Or either that someone has some mad selling skills.
EDIT- for the MP3 player (This is just a wild guess) regarding ipods and such, I wonder if other stores that have high AAR are adding attachments for what's inside the package? for example sometimes there are camera sets (Case, SD card, etc) they could be using those extra items that are in a bundle and adding them in as AAR....against policy to do that too...just a wild guess though as to why they could be having high AAR.