AAC is a lossy format, regardless of who sells it or what encodes it. FLAC, Apple Lossless (ALAC), AIFF, etc (I believe WAV is too), are examples of lossless audio formats. AAC, MP3, etc, are lossy. Best way to tell - if the files are, say, 4MB or 5MB for a 3-minute song, it's in a lossy format. If they're more along the lines of 30MB-40MB for the same song, then it's lossless. The online stores steer towards lossy files because, one, they take up less space (therefore not putting as big a strain on your connection - a 70MB album compared to a 700MB one), and because they're more likely to be supported by other players (for example, iPods don't support FLAC or WAV). In the end, in most cases the noticeable difference in quality between a lossless file and a lossy one (say, an AAC file encoded at 320kbps), is negligible.
(Btw not all this post was aimed at you, the rant at the end was more a guide for people that may not understand the difference )
I agree 100 percent. And I knew all of that - just didn't feel like pointing it all out. But thank you for doing it so I didn't have to