Other than the Steam review system, surprisingly few. Pretty much every social media you can think of (and YouTube and comment section) already existed when Civ IV released. What's changed, of course, is that by and large none of them had hit their exponential growth phase, so the mass of people on each of those services wasn't yet where it would be around the time Civ V released.
Which ultimately I suspect is where a lot of this shift happened - the growth of community naturally caused the number of what I might call "possessive" fans to grow, until it went from a tiny fringe of two or three curmudgeon easily ignored into a very visible vocal minority of a couple dozen voices actively involved in every discussion and reinforcing each other. The increased visibility helped normalize that kind of fandom-possessive reaction, making more people embrace it (to avoid getting drowned out by the louder voices, and because it's more emotionally satisfying, among other reasons). More people embracing it gave the possessive attitude in turn even more visibility, and normalized it even more, etc, etc, and, absent any measures to check that kind of possessiveness, it just became an accepted norm.
(and, because all those sites and communities were interrelated, even if one site DID take steps to check the possessiveness, it would continue spreading everywhere else and new members of that one site would still join with the exception that the posessive attitude toward your fandom was how things should be, leading to complaints about not being allowed to do that, etc, etc.).
In effect, a normalization critical mass, if you will.