There's a lot more to the cost of upgrading than the price of the license. Licenses for Win7 are nothing compared to the price of upgrading all the custom software they developed over the years to insure compatibility with a new OS. The reason almost no business or organism decided to leave XP for Linux is because it's not economically advantageous to do so. When talking about an investment as big as this, you can be sure that almost every options have been evaluated.