The reason there are so many patches is twofold.
Firstly, Microsoft take a much more proactive approach to security than Apple. An Apple fan might tell you that's because iOS and Mac OS X suffer from fewer security vulnerabilities. This is of course, completely false. A whole range of security issues are regularly and frequently discovered in both of Apple's key Operating Systems, but Apple prefer to hold off on releasing these and bundle them into bigger, monolithic updates, or indeed simply not release them at all in favour of bundling them into the next product update. Apple do this in an attempt to maintain the illusion their products are more secure.
Microsoft by contrast release updates much more frequently. Microsoft's 'Patch Tuesday' approach gives business users predictability as to when security patches will be released, allowing them to schedule their patching processes accordingly. For consumers, it also means you get a product that can be kept more secure - patches are a part of life if you want a secure product.
Of course, not all patches are security patches - plenty of patches are to improve performance or stability too. Again both Microsoft and Apple handle this differently. In iOS for example, it's pretty rare that you see any kind of minor patching going on to update performance or stability unless a major problem is disvoered. In OS X, Apple do release updates on a regular basis. Microsoft prefer to push out smaller updates monthly, but hold off on a bigger set of improvements until they're ready to release a Service Pack or other kind of major update (as is coming in Windows 8.1).
Why do Microsoft hold off? Well, the reality is that Windows is in use on a broad range of hardware out there, with a vast number of different configurations, and so it's good practice to test all the updates and improvements thoroughly, ensuring that they work well together as well as just standalone.
In short, there are more patches because Microsoft care more about fixing things fast, but in a sensitive way that makes sense. Apple prefer to hold off as much as possible and turn their updates into product launches that their CEO can brag about in front of an audience. Microsoft are kinda doing this too - but at least in the meantime they keep on top of their security bugs!