One hears the same 'dividing the player base' argument with Bohemia Interactive's ArmA 2 community every time an expansion/DLC is released. As far as I can tell, people tend to upgrade to the next version of the software sooner or later, so from that point of view, it is pretty much a non-issue. Mods, if anything, 'divide the base' far more, as do private servers, clans, exclusive friendships, time zones, language, nationality, and other factors. In other words, no group of players is truly homogeneous for any game, and the factors that divide the community are as often as not outside of the dev's/publisher's control. This is to say nothing of we single-player only types; when it comes to gameplay, we, at any rate, are as divided from the rest of the player base as one can get without actually playing something else.