Have you noticed that those numbers don't include the PC version of RE5, RE6 and RE4? Now you did!
Resident Evil 6 is only included as "PS3/Xbox 360/DL" and "PS4/Xbox one/DL". Same with RE5. The PC version for both games were released a couple of months after PS3/X360 release and they were considered as different SKUs. Resident Evil Revelations 2, on the other hand, has "PS3/PS4/Xbox 360/Xbox One/
PC/DL" in its platform listing, since the game released simultaneously on all platforms and it was all considered as a single version of the game.
From SteamSpy:
* RE6 (both digital and box version required Steam activation): 1,070,940 ± 30,498
* RE5 (doesn't include GfWL copies that weren't activated on Steam when the game was released): 902,887 ± 28,009
* RE4 HD (the old Sourcenext version not included): 714,339 ± 24,920
So you can up those numbers a little bit in the OP