I started playing CSGO a week ago after watching a lot of streams and it is extremely difficult, I agree. Even the basics.
Back to the topic:
I wonder if they count all the expansions into the 4 million (basic game, western front, ardennes assault etc). Because then a lot of people bought 3 copies of the game. They probably did.
I also wonder where all the people went. CS got 2 million more copies, but has around 300k people playing it most of the time, compared to CoH2s 5k.
Somebody may have said that before, I refuse to read 8 pages of forum posts
Summerized: Don't ever trust statistics that you haven't falsified yourself