Why are existing songs updated sometimes?

Question

Does anyone know why it happens that, during a sync, I will get a message "updating files on _'s ipod" and that it is copying songs that are already on the ipod. Usually it is just a few song, but in my most recent sync it was 109 songs, all of which (with the possible exception of one) were already there. When it was done, my number of songs and space used was the same (except it showed one more song).
Other times there were no additional songs at all. In case it is relevant, I sync specific playlists.
No big deal. Everything on the phone has been working perfectly and it syncs correctly, I am just curious as to the technical reason for the behavior.

Answer 1

...because if you update the cover art, the song information (including comments, or add the song in question to another playlist, etc) it has to duplicate that on the ipod... so something or someone (if not you) is making changes to those songs, even in some small way. The iPod syncs every little bit over, so something must be going on... It would only update 'play count' on your computer, not on your ipod, but sounds like cover art or comments or somethin else...
-B-