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Even if you pay money for the windows 10, it is unlikely to even start on the hardware that XP ran on. Not only will the people have to go through the budget to pay for the software, but now you need a full upgrade plan.
To put this in a concrete example. If a hospital had a check-in system running 12.04 they could just take someone internal from IT and go and fix it. If it was Windows XP then they need to go through finance, then get a offers from competing companies, fitting the upgrading into the budget, and last have people installing it in each of the hospitals entrances. The first case has a project length of days and the other of months and in worst case years.