I have a 2nd gen Ipod that sometimes updates the play counts, and last played dates when I sync it to Itunes, and sometimes does not. And yes, I checked the clock and date function to make sure it was set.
I think I have stumbled across the cause, and it appears this also affects 3G and 4G Ipods as well.
Anytime the Ipod reboots (or resets) it looses all play counts and play dates of songs you have played since the last re-sync. So if you play 10 songs and reboot the Ipod and then re-sync to Itunes, the play counts and last play dates will not be incremented in your Itunes library after a re-sync.
Others have reported this behavior with 3G and 4G Ipods after they go into the deep sleep mode, and I believe the real cause is that they always reboot after entering a deep sleep. It appears the cause is the rebooting process which kills the play count and play dates stored in the Ipod.