Because 7 8 9.
XP Edit: Explanation(http://en.wikipedia.org/wiki/ChiRho)
Window.
All the extra cubholders.
A potato wedge! (I made this up when I was 9)
Because they don't exist
Because chickens didn't exist yet.
Hey Microsoft, why is there no Windows 9? You've given us 7 and 8, and now you're skipping straight to 10?" "Well, to be completely honest, 7 8 9."