And you totally missed the point.
Which is what? That everyone should be nice and support everything they've ever produced until the end of time? At some point, supporting legacy systems begins to take away from advancement. Would you rather dedicate resources to solving new problems and inventing new things, or regression testing patches on systems from 15 years ago?
Maybe you know more than I do about what goes on inside Microsoft, but I think you're making some assumptions that aren't necessarily true. You say it's a small price to pay, but it does add another whole OS to support (granted, this is somewhat reduced while Server 2003 is still being supported). It may be a much larger price than you believe. You also imply that simply perpetuating the XP status quo is a good thing. Keep in mind that XP was released when 9% of US households had broadband (compared to 72%+ now). It was before the 130nm 1.6GHz Northwood P4 was released. Consumer dual-core CPUs were years away. Newer versions of Windows are designed to work with modern hardware. If your XP system is truly incapable of running Windows 7, a new PC would probably benefit you in other ways too.
For what it's worth, it seems they've provided much more support than Apple, who already dropped 2009's Snow Leopard from getting updates. Windows 7 is only a few months newer than SL but will be supported until 2020.
No wonder american businesses don't give a flying f about anything but their bottom line. Apparently, customers don't either.
A capitalist business exists to make money. I expect any company to attempt to maximize the amount of money they make. That doesn't necessarily mean charging the highest possible prices for the minimum amount of product/service, as life is more complex than that. There are things that are mathematically good for profit now, but may affect the company long-term or in unrelated ways, and things that don't look as good on the books but help business overall. But yes, I expect Microsoft to draw a line when they decide that it's costing them much more money to keep supporting a product than they will ever make from any resulting goodwill of doing so.