The flaw in their plan is that the intersection of people capable of figuring out how to pay a ransom payment in Bitcoin, and people still using Windows XP, is pretty small.
Turns out that for a lot of victims wiping their old computer was deemed less expensive than the cost, nuisance, and risk of paying criminals through some shady internet fake money thing to possibly avoid having to wipe their computer.
For anyone with a recent backup of their data, I can't think of why they'd pay.
HN'ers might, but HN would not be a representative sample.
Problem -> Reaction -> Solution.