Undoubtedly a larger percentage of PC users have issues. There are a few reasons for this, almost all based around the simple fact that PCs aren't 85% of the market, they're 93%, give or take 2%. Macs are 5%, Linux/Other is 2%. That's an enormously large difference.
1) This makes it so that developing malware is a no-brainer. If your effort can hit 1700x as many computers by making it for PCs over Macs, you make it for PCs. So, while the level of Mac viruses are going up, and while Macs tend to really be no more secure than PCs, there's simply fewer people looking to exploit those flaws.
2) Since there are so many more PC users, there are more PC developers. And since PCs are a much more open format, letting you think differently, and since Microsoft doesn't strictly force manufacturers to bend to their whim, allowing vastly more hardware choices, you end up with things that don't work together well. Remember all those blue screens of death (you've probably had very, very few since Windows 98), those weren't Microsoft's fault, they were hardware manufacturer's fault. Your new graphics card was sweet, but it didn't play well with something regarding your web cam's drivers, or some other software. Microsoft not being anal like Apple meant far more choices and more competition bringing up quality and down prices, but also meant that not everything functioned happily together.
3) Let's be fair, with PCs being cheaper you're going to get more completely clueless people using them. They're ubiquitous, and people kind of need to sort of know something about technology to even realize to go Mac. So while some true morons go Mac, most stay PC. If you're halfway qualified to properly think about technology you probably have little malware and virus trouble - you know how to avoid it. People like my parents do not. They never seem to learn. As a result they have far more issues than your non-tech-moron user.
4) Lastly, tying sort of into #2, PCs are cheap. Cheap PCs are extra cheap. To make them so cheap costs are cut. An inferior motherboard is used, less quality RAM, insufficient power supply, etc. If you want a $250 laptop this is what happens. So all those people buying emachines gibberish from Walmart end up with serious hardware issues and wonder why, blaming the PC platform. Some, rather than realizing it's because they bought lowest tier stuff and buying properly, run out and buy a Macbook costing 5x as much, then when they don't have the same flaws they praise the Mac. They don't realize that a $600 PC laptop, still a third the cost of the Macbook, would also have avoided these issues. It's like thinking your $10k Geo Metro breaks down too often so you run out and buy a $50k Lincoln when a $25k Honda would have worked every bit as well.