Cover.jpg is a default in Squeeze Center. Hardly "odd" at all.
From the settings/behavior page:
"By default, images named "cover.jpg", "folder.jpg", "album.jpg", or "thumb.jpg" are used." I had issues with album art only because I use cue sheets (i.e rip full flac albums with cue files associated) but I simply name my jpg the same name as the flac or cue file. it works fine, as does imbedding using MP3tag (nice free program).