Which operating system needs to be restarted?

Every time I talk with a UNIX zealot about the advantages and the drawbacks of Windows he always says: "Windows needs to be often restarted".
Recently I was reading about MacBook Air anche RemoteDisc and I had to notice that if you install RemoteDisc services on a Mac you need to restart the Mac before using RD... well this is not necessary if you install the same services on you Windows PC!
So, which operating system needs to be restarted?! It seems that it isn't Windows!