There's been, and probably will continue to be, quite a bit of debate about whether or not MMOs should have centralised official forums or should let fansites take the burden of operating forums for community members. On the "we don't need no official forums" side is NCsoft's Tabula Rasa, which uses fansites directly, and Mark Jacobs of Mythic, who doesn't hold official forums in particularly high regard.
On the "we have official forums; come to them" are pretty much every other MMO on the market. Quality of the official forums varies wildly from game to game, with some MMOs having more popular fansite forums than official forums and visa versa. In general though, most players probably start off in the offical forums since that's the logical place to begin.
With due respect, any MMO that thinks they can operate without official forums (or something that is so close to a forum-style communication structure) is deluding itself. Jacobs is technically correct about what official forums contain, but he misses the point - that these are his customers talking to each other and sometimes to him. Most of the time, what these customers say is pretty high on noise, but that's how the internet works - you have to plow though the noise to find the signal, and sometimes the signal comes from surprising places. Having a centralised forum allows a MMO to develop a community - which is, compared to just offering a gaming experience, probably more important to the long-term health of a MMO. Communities can be sticky things. They hold players to the game long after they would have quit if they were only considering how much they were enjoying the game.
Of course, fansites can do the same thing with their forums; fansites can certainly build communities. But, in my opinion, fansites work better at creating common-interest communities (e.g. a guild, or the role-players, or the PvPers), not large sprawling all-in communities you see on arise on official forums. Having 100 splintered fansite communities doesn't make it easier to communicate to them or listen to them; it makes it harder. If there is a fire to fight, the community manager staff have to (or: should - sometimes they think releasing a PR statement on one site is enough, but it doesn't work if different fansites run off on different tangents) deal with it in numerous places at one time, rather than dealing with everything in a central forum.
Also, it might not take much for the operator of an officially-sanctioned (or close enough, if they've been favoured with interviews and exclusive content) fansite to turn against the MMO it follows. It might not be much - a mail-out that they don't get, a rude PM from someone on the MMO staff following some fansite forum comments, a nerf to the operator's favourite class or item - but suddenly you have an uncontrolled (and uncontrollable) rant site that has in the past been given a lot of official credibility. You can look at the EQ2Flames drama for an example of this.
Forum drama does create epic lulz, but like most clowns it isn't really that funny.
So, not only does the MMO team lose face as the operator rants their little heart out (sometimes spilling privileged information they know) but a relationship has to be built up with at least one other fansite so that players will start hearing the 'correct' dev message again.
Having a MMO without an official forum is like having a zoo with no fences - you can't control where things wander and feeding time can turn very messy indeed. An official forum at least keeps the majority in one place and lets communication occur more easily. There will always be some fans who prefer fansites - that's fine. But those fansites tend to closely follow the information on official forums and, if those players want to get heard, they know they need to comment on the main site.
If official forums suck, it is because they have been allowed to suck by the community managers (CMs). CMs have to draw a line in the sand and say, "This is too far," then act when players cross that line. If the WoW official forums suck, it is because Blizzard doesn't care enough for them not to suck.
There have been cases where official forums have been criticism-shy, deleting every negative word that might appear. This is stupid behaviour. Some criticism of the MMO is necessary, even desirable, because it will point out what players feel is important. Who knows, the group consensus of the players might be right? Fansites might not be nearly as well managed and discussions are likely to be between smaller groups of people who already mostly agree with some key issues (e.g. PvPers tend not to care what the RPers think, and visa versa), so their criticism is likely to be slanted heavily and not examined objectively.
If MMO CMs / devs want to stop the majority of negative behaviour that goes on in a forum, all they need to do is remove the anonimity. Make people post under their real names, even if it is just a first name and initial. Well-run official forums actually require CM and dev interaction too - if you leave a zoo as breeding grounds for the bored and restless because you give them little to do, you shouldn't be surprised when it produces only manure.
As more people start playing MMOs - and as the MMO category expands to include more people playing different types of games - I'm sure the debate over whether or not the effort of officially managing communities is worth it will increase. In my opinion, it is, and the cost of running official forums is well worth it for what it returns in information and customer involvement in a MMO title.