Except you're using popular series' that have retained the expected amount of players that you would assume those kinds of series retain.
If 100 people buy a game and 2 are still playing it at the end of a month, how many people do you expect to still be playing a different game at the end of a month when only 10 people buy it initially?
Except that my point is that Splinter Cell for example has sold around the same as this game will probably sell.
And more so, we're talking about a game launched 2 years or 2 years and a half ago vs. a new game after 1 month.