iPod Play counts between iPod and iTunes

[Astral Cars]

So what is the deal with the iPod transfering play counts to iTunes. It seems sometimes or some songs rather get updated in iTunes and others don't. For example, I listened to an album on my iPod and also another single song later. When I synced them the play counts on all the songs from the album stayed the same, but the single one added one to the play count in iTunes. So, how is the play count kept track of on iPods and what makes some songs update and others not?