1) as said earlier, alot of people who play games on Steam do so in offline mode.. many service Providers have "Bandwidth caps" that limit how much data they can use a month before paying overage charges.. playing Steam games in offline mode helps save data
2) it did not say 5 million, it said 6+ Million daily.. remember, not every gamer can play games everyday.. there are things like Jobs, Family stuff, going and shooting some pool at the local pub.
3) you are still not taking into account those playing games that are not Steam games.. for example, all those playing games by EA are using Origin (like the BF4 you mentioned earlier), those playing any game from Ubisoft (assassins Creed, Frycry, etc) is currently going through UPlay.. alot of the Bigger PC Games (like League of Legends, Planetside 2, World of Tanks) all have launchers of their own.. then we have GoG, which is quite popular these days as the source for retro games, which has no DRM service at all..
and you said your a MMORPG gamer? How many people do you think are logged into WoW, ToR, LOTRO, Everquest, RIFT, Eve Online, Diablo 3, and all those FTP MMORPGs at any one point? as they are all PC Games
total that all up with Steam, Origin, Uplay, and even those games that have their own launchers, and it is going to likely eclipse that number of CoD Players you keep mentioning..
I couldn't have put it better myself