iMac with Mavericks sometimes won't sleep
backupd is most of Time Machine. I think your computer is constantly backing up over a slowish network link such as WiFi.

I suspect that you have a large amount of file changes every day. Is the Windows image you are running in in Parallels being backed up? That could do it? Go into System Preferences > Time Machine and click on Options...

This will allow you to exclude your image files from Time Machine.

If that doesn't work turn off Time Machine for a couple of days and see if the computer sleeps.