Can someone, with figures and references to original data, please explain the *75%* in the title of this thread?

I'm looking at the OP, and I'm not seeing that.
I consider the 'population' to be the 'average' population excluding patch peaks. The average seems from those figures, pretty unchanged.
I'm starting to think the biggest problem is that we have 'way' more servers and DCs, and the population has shrunk as much as it's grown, ie it hasn't grown. Leading to hollowed thin spread communities.