Oh, I should probably point out (if it’s not obvious by now) that I’m a complete noob when it comes to music and its, let’s say, "technical" side, so if that’s the most stupid question ever asked here, sorry.
I think it might have been like that since…ever, I mean that date and all. I just realized it now and got a bit freaked out by that. Maybe Winamp isn’t cut for such files? Because with standard MP3s, I can go to file info and check Basic Info, Artwork, ID3v1 and ID3v2, while with M4As all I can do is Basic Info and Artwork.