Microsoft's never ending rant about OEM resellers of Windows. It's their own damn fault.
Microsoft doesn't fancy the reselling of their Software. Specifically not Windows. They fight an endless battle that has occupied countless judges. And usually they lose. While Microsoft sells their current version of Windows 7 ( professional ) for ~309€ you get it for 160€ or less as resold OEM. It's the very same product. There are no bells or whistles attached to the retail version. These licences are usually snagged from bulk volumes or they are simply not ( or no longer ) required for the product they were originally shipped with. This of course is a drain for Microsoft. OEM Versions have basically taken over the specialist supplier market. The retail version pretty much is only available in electronic markets. They usually sell it around 280€. I'd suspect not in volumes...
The situation is Microsoft's own fault. Entirely. It's their price policy. 309€ for Windows 7 Pro basically is a bad joke. OS X upgrades ship at under 20€. I actually have problems to find a retail version. Let's just say it isn't really important if it costs 40 or 100€. It would both be cheap in comparison. And you can install it on any stupid Mac you might own. You can only install Windows on specific platforms and not in numbers.
Now of course Apple sells Hardware and Microsoft doesn't. So a lot of the price in OS X is cross financed. But that's a somewhat screwed view as Microsoft also sells Office and a lot of other things running on Windows and pretty obviously you'd need Windows to do that. If Microsoft would simply stop being stupid they would drastically reduce the price of their OS. It's not that they would actually lose a dime. If I could get a retail version of Windows for 160 from Microsoft. Why the hell would I want to buy one for 130 from some shady source?
The OEM versions drastically reduced the amount of illegal copies of Windows. That's all copies Microsoft only made a couple of dimes with...if any and obviously they didn't make much with the illegal copies at all. And it's all because of their price policy. How stupid do you have to be as a consumer to buy a product for 309€ when you can get the very same product for 160?
Now some people argue that the price for OEM ( not bulk ) is tailored to the device lifespan. The device is supposed to be replaced after - let's say 3 years. Windows however has a much longer support. So by buying OEM Versions you kinda cheat yourself to an extended service. This is bull for various reasons. For one the new box most likely comes with a new bundled Windows. Stock sells rarely ever come without OS and - unless you buy a Mac - that's Windows.
Looking at my license box that's two copies of W7 pro, one for XP and one ( never used ) for Vista. I also have some "vintage licenses" in there. I of course could sell them. But who buys a license for XP today? I could give it away to someone for free. Same with Vista. But I doubt anyone would want that and I need the two W7 licenses. If Windows 8 wouldn't suck I could of course again sell them. But who buys W7 licenses in a W8 world ( assuming it wouldn't suck )? And for what price? It's simply a delusion that people who actually buy software licenses stick with an old system when they buy a new computer. And even those who do rarely sell their licenses. Most consumers who actually do sell their licenses are probably guys wanting to make a statement. Linux users who never wanted the license in the first place for example.
The big drain comes from OEM versions that - for example - were supposed to be shipped with a new computer. Microsoft makes money with this. Even if the software is never used. Now they bitch that their partners are 'abusing' the system. Well. Welcome to the real world where you can have one or the other but not both.
If you want to sell stuff to consumers you need to make an offer they are willing to take. 309€ is no such offer. If you want your product on every computer that's sold you need to go OEM. If they get your product significantly cheaper then it's pretty much natural that they get the idea to sell it.