I just figured out what was causing my Mac Pro to stay awake.
It was *Drum Roll*
Paragon NTFS (I have version 7.0.2 but this seems to happen with earlier versions too) apparently if you have it installed it causes the mac to stay awake although a manual sleep is still possible. If you have it installed you have to uninstall it for the Mac to sleep by itself simply disabling the driver doesn't work.
According to a MacUpdate member, BARQSX, this problem doesn't only affect Paragon NTFS but MacFUSE as well (
http://macupdate.com/info.php/id/26288/ntfs-for-mac-os-x ). Although you need NTFS-3G in conjunction with MacFUSE to write onto NTFS drives for free.
I have MacFUSE installed on my system for use with VMware Fusion and it will still auto sleep as long as Paragon NTFS is off the system.
And a small side note it seems like having "MenuCalendarClock iCal" app causes the system to stay awake as well as Firefox, so quit them for auto-sleep.
Too bad, I like and need Paragon NTFS so I'll just have to live without auto-sleep. Hope this helps anyone experiencing the non-sleep issue.
Just one more thing I set my system to check if it would auto-sleep after 1 minute after quitting all apps and uninstalling Paragon NTFS, the screen shut off after one minute but the sytem didn't auto-sleep till about 4 to 5 minutes later even though the screen and computer were set to sleep after a minute.