[Freddy]

When Microsoft announced its newest operating system, the surprise was not that it was coming, but that Windows would be skipping 9 and headed straight to 10. When asked about Windows 10’s name, Microsoft didn’t give a clear answer. So why, exactly, is Windows 10 getting the nod instead of 9?

http://www.extremetech.com/computing/191279-why-is-it-called-windows-10-not-windows-9

[Data]

I have a theory.

Nine sounds too much like German for no "Keine".

Windows ... No

[Freddy]

  that might be nearer the truth.