I'm going to take you at your literal word here. You've never run a malware scan. You've never run a virus scan. You've never had to defrag your drive. You've never had to run a chkdsk. You've never had to clean out your registry. You've never had to do anything to maintain your computer.
All of these things count as productive time wasted at an average of $12/hour for the user and an additional $25/hr or more for technician costs ($90/hour if you call the Geek Squad or some of the other commercial service shops.) Even assuming that you only do some of these things once a week, others once a month and the most extreme once a year, that adds up to a minimum of 65 hours lost at approximately $37/hour for over $2405 in maintenance costs for the average PC.
Granted, you, as a Geek and a technician/professional don't see the direct cash outlay, but a business will see that in lost productivity by the user plus IT costs for maintenance. If you had to put a monetary cost to every minute of downtime you spend doing routine maintenance, the numbers would add up, and quickly.
I don't deny that some of these same preventative maintenance measures may be helpful on a Mac in OS X; but for now, the down time for such maintenance averages less than one hour per month--totalling maybe $444 in a year, almost 20% of the maintenance cost of the average PC. This does not take into consideration energy savings (if any, and I know there is) you would experience with every model of desktop Mac compared to any desktop PC.
You may not be aware of it, but the bean counters are.
Why else would 50% of enterprise in the US and worldwide be looking at alternatives to what they are currently using? Why else would 12% of these already be implementing a changeover from Windows? The snowman is melting, and that rate of melt is accelerating.