Sleep isn't a no-power mode, it's a very low-power mode and as such there's power going through your PSU. While it's not much, turning off the fan could lead to a buildup of heat within it, and that's never good. It all depends on how the PSU is designed.
Stop wasting electricity and get Hibernate mode going on that system. Uses no power and boots up almost as quickly as sleep.
Hibernation's not going to work, it takes about 2 minutes for my computer to come back up and that's way too long. Besides, electricity's dirt cheap in Vancouver
As for S3 and S1 states, I guess that's accessible through the BIOS?