Consider a machine shop that is family owned and operated. Much of their equipment was bought in the late 1990s. Say they have equipment that runs CnC lathes that can only accept jobs from networked PCs running NetBEUI. Consider further that the company that manufactured the equipment is no longer in business, so there is no one to rewrite the code in that lathe.

The company in question cannot upgrade to Windows 7, for there is no NetBEUI support. The company cannot afford to pay out what would amount to seven times their yearly gross to upgrade their equipment.

Now consider the number of companies in this situation. Windows XP still accounts for more than 20 per cent of all detected Windows computers connected to the internet.

So what would it take for Microsoft to continue support? Let's say that they need 50 full-time programmers to provide ongoing patching support for Windows XP. Let's also say we give them some hefty incentives in the form of $500,000 a year, and then double that to account for good benefits and administrative overhead.

That equals $50 mil as the cost of ongoing yearly Windows XP support for Microsoft.

Estimates are that there exists 1 billion PCs in use on the planet. 20% of those are running XP. That means there are 200 million XP boxes floating around. Let's further say that 99% of those are still using XP due to "cheapness". That leaves 2 million Windows XP boxes that have a good reason to keep on being XP boxes.

Microsoft sells Windows Professional for a three year cycle. The cost is $200 or $66.67 per year. Assume further that all 2 million systems pay the cost to remain upgraded. Do the math and you have $130m a year. Deduct the cost of $50 million and you have an $80 million profit.

Plus you haven't figured in the good will it would produce.