Sure, it might have the most DRM-free tunes from the major record labels, which translates into more tracks that you can copy onto your iPhone, other cell phone or just about any device, but Amazon's MP3-only music download store still can't seem to take a bite out of Apple.

Ars Technica reports on some research from the NPD Group showing that only 10% of the folks buying music from Amazon MP3 came over from iTunes. Instead, the report says, Amazon MP3 seems to appeal to different demographics than iTunes.

Then again, NPD points out, as the top music retailer in the US, the iTunes Store sells ten times the music downloads as Amazon does, so it might not even feel the little nibbles Amazon makes.