That, to me, is the big difference between Macs and PCs.
I built my PC myself. Runs XP. I haven't rebooted it since I moved into the new apartment two months ago. It runs 24/7. I've had Windows-based machines running for months and months without requiring a restart.
The horribly misconfigured machines you use at work should not be used as an example.
Think of it this way: if Microsoft had only a few different hardware configurations to worry about, Windows would be much simpler to build and maintain. Since they have to build an OS that works with literally thousands of different pieces of hardware, the fact that it's bloated shouldn't surprise anyone.
And yes, Macs have fewer virus and security issues, but that's not because they're inherently more secure, but because virus writers and hackers want to make the most trouble on as many machines as possible, so they target Windows. If all those troublemakers suddenly turned their eyes to the Mac, Apple would have just as many "issues" with their OS as Microsoft.