It's claimed it was optional, but in fact, a good deal of functionality was and still is tied to it. They've made it "optional as long as you don't want to get too involved in the community".
As things stand, now that they've rescinded the decision to force the use of real ID's on the forums, you can still be just as active in the community without sharing your real name as you could before.
I think one of the problems with the whole real ID idea is that it ignores what makes it possible to create a community online out of a bunch of strangers. In my opinion, anonymity is actually something that allows people to interact online in ways that let them become an online community. Yes, it has it's downside, with people feeling free enough to be complete and total dickwads. But that same anonymity allows people to feel free enough to speak openly about beneficial subjects as well.
Thing is, online we don't have the tools that we do in face to face conversation to decide whether or not someone is a good idea to talk to about our lives. In the real world, I can look at someone, and see how they're dressed, if their hair is cut, if they've showered within the past 3 days, read their body language, tell if they're brandishing a machete, and make a judgement about whether or not they're dangerous or not, or trustworthy or not, or sane or not. Sure, that judgement may not be totally accurate, but it's going to be a lot more likely to be accurate than if I cannot see or hear the person I'm talking to, and have nothing to go by other than text. Without being able to make that judgement, it can be very hard for a person to feel comfortable revealing anything about themselves. Especially if that revealing about themselves is actually tied to themselves in a traceable manner. I mean, I don't even give my full name out if I meet a nice person in a bar -- and I've been able to judge them well enough to decide whether or not I want to give them my phone number.
Knowing that I can't be identified easily (yes, I'll throw that caveat in there -- people can be identified if someone tries hard enough, long enough) makes it possible for me to talk about myself, my life, my point of view on controversial issues, with these complete strangers online. That anonymity is what actually allows me to build relationships with them. That very same anonymity is what allows me to participate in the building of a community in the first place.
Now, I'm not saying that community building online can't happen unless everyone is anonymous. I'm sure there are online communities out there who use real names and do just fine. Thing is, the ones I know about are a) very very small in comparison to WoW, and b) related to a real world subject -- for example, being a professional writer, where you WANT to publicize your name so that people can read your work. WoW has neither of those two aspects.
You have people of all ages, genders, races, religions, localities, professions, past times, etc. who play the game.
Millions of people with nothing in common other than this fictional role playing game where the whole point is to
not be yourself. A game where, on some servers, it is
against the rules to make real world references in open chat. Where it is
against the rules to name yourself after a real world figure. Suddenly requiring people to converse with their real names... It's beyond counter intuitive. It goes against the entire spirit of the game.
But, thankfully, for now (yeah, for now... who knows what the future holds on this subject), real names are not required. The real ID system doesn't have a whole lot of functionality currently. Not that many people even use it (based upon my own insufficient sample). Those who do use it have reported that they're not real happy with it, because it reveals wayyyy too much about where they are or what they're doing online (no more hopping to a lesser known alt on another server to escape your annoying friends for half an hour -- they know all your characters now, and can message you anywhere on the battle.net network), as well as that it reveals your real name not just to your friends, but to friends of your friends -- people that you may not know, and don't know what they'll do with your info. All it is right now is a fancy inter-realm communication system. An instant messenger that uses real names. There's not much "community" that you miss out on by not using it.
We have a thread in the Members Only computer gaming/entertainment section here too 
) or some deranged kid searching for a gamer girl to stalk, or whatever, really.