As of yesterday, Microsoft stopped supporting Windows XP service pack 2. (And Windows 2000, but no one cares.) Weird thing is, the company also says that 74% of Windows businesses still use XP, and a lot of us must, too. Why? The company's handling of OS upgrades sucks.
Well, that and Windows Vista launched to horrendous reviews, making folks understandably nervous about upgrading. Still, a lot of those XP users didn't make the jump to Windows 7, which was well received.
So, what gives? Really, it comes down to one thing: price. If you have a Mac and want to upgrade to the latest version of Apple's OS X, Snow Leopard, it'll cost you $30. That's in comparison to the $100 it costs to upgrade to Windows 7, or more if you're getting into the Windows game for the first time.
Now, for a business, things get a little more complicated. They've got security to worry about and old hardware that's not up to snuff, but also issues such as proprietary software not working on the new system. For you and me, though, $30 is obviously infinitely easier to stomach than $100.
Launching a new iteration of Windows isn't cheap for Microsoft, but if the company really wanted to recoup its losses it'd make it a no-brainer for home users to make the jump. Don't flood shelves with a billion confusing flavors of Windows, and don't make upgrading expensive.
Be more like Apple: come out with a clear choice for Windows users, make it cheap and make it easy.
Now, that said, hopefully Apple will continue learning from itself. The company has charged as much as $130 for previous versions of its operating system (though, sometimes, you'd be eligible to get it for free), so hopefully Apple continues to keep it cheap as well.
CORRECTION: As pointed out in the comments, Microsoft will still support the latest revision of Windows XP, which is SP 3, or service pack 3.