I'm going to go for a different approach on the matter. I don't think there is A Community (agreeing with many posting here), but a lot of different kinds of communities, with different levels of interaction. Basically, any IC channel (and some OOC) with steady amount of people (not necessarily the same) will turn into a community of it's own. It doesn't have to go along racial/faction lines as Louella pointed out, but indeed it often does. But I believe it relates to closure, so there would be four kinds of communities:
-Closed communities: a settle group of players, often being the same, with specific traits that make them appropriate. An IC RP channel for members of a corp is a good example of this, but it can also be any IC channel with password, or set list of blocked/allowed people for other reasons (for example, let's imagine someone's house always has people in it, it would turn into a closed community but not along corp lines, but all being bond by friendship to the house owner).
-Semi-closed communities: semi closed communities are those that anyone can theoretically access, but in the end catter to the same people always and have heavy moderation in place. A public corporation IC channel is one such example, but also heavy faction-only channels (like the chapel).
-Semi-open: these are the other side of the coin from the ones before, channels open to anyone and with a big allowance to people coming and going. Still, a more or less stable community has developed around them, and though they don't block anyone's access, it may require some time to know the protocols, who's who, etc. A classical bar channel would be an example of this.
-Open: finally, those open to all, with little to no moderation, where everyone is allowed. The Summit is the best example of this, of course, but not the only one (Live Events, OOC, the one Silas had created as an experiment, etc.). They have a open theme with little details, so the effort of entering the arena is much smaller, mostly requiring people just to be IC and a few more things (like the slave issue in The Summit). Other than that, almost everything is game.
With this in mind, I believe each and every one of those are separate communities, though a player often belongs to a lot of them and quite often they will overlap. One can be in his closed corp IC channel, at the same time in the public version of it and also on a couple loyalist-only to their faction, then a few bars they like, and finally the Summit.
So there is no The Community: players that may be important in one may mean nothing in another, for example, like rules of what is fair or not, what is allowed (big difference, for example, is it a physical place?), etc. There are dozens of communities interacting along the lines of players moving from one to another, bringing the baggage their characters have been developing, and interacting with others like balls on a pool game.
If there was to be A Community, the only one I can think of is out of the game: IGS, as it is the only central hub for RPers, with no equivalent. And, even there, lots of awesome RPers don't post or rarely do so, players who may be very important in other spheres. So I, personally, would only consider IGS the biggest Open Community of all, but just one more among many.
As for gates, sure that The Summit and IGS are some big ones, but not the only ones. A corp recruitment channel can surely be also someone's gateway (was mine, together with the Amarr faction channel which, back then, was quite full of RPers), specially to newer pilots that are looking for somewhere to fit both in RP and also game-wise. And I'm sure many other doors exist (like a bar, for example, for a publicized event in IGS that may draw curious or interested people in RP).
