Does a game need an unbeatable monster?

Rawrsaur sent me a link to a video Square Enix released on how to beat Absolute Virtue, an uber monster in Final Fantasy XI, which hasn't been beaten yet in a legit way. He writes:

Absolute Virtue is essentially the pinnacle of FFXI raiding. Nobody's ever defeated it. They've datamined it, they've tried all sorts of things, but to this date, given the (roughly) 500,000 subscribers, they have yet to kill the thing. And it hasn't been for lack of time, either. According to the wiki history at ffxiclopedia.org, the thing's been around since january of 2006. It's been around for two entire years, and nobody's been able to take it down legitimately.

The developers have not nerfed the encounter. Most of the information has been data mined about the creature from the game files (it is effectively 9 levels above players, it has around 120,000 hp, etc. etc.). They know what it drops. They know what it can do. It is just tuned to the point that killing the thing is nearly impossible.

There were a number of glitches that allowed some players to defeat it.

So what do you think about something like this? Obviously, this monster isn't meant to be part of some sort of loot progression line. That's something FFXI never really did. The loot you can earn through raiding is a little better than the loot you can earn through grouping, but it isn't huge amounts more. There have been recorded attempts... as few as 18 people, and as many as 320 people all gathered together to try to kill it, and all failed.

Do you think something like this would fly in the present day? FFXI is niche; they had their day in the sun and they still do decently well (I love the teamwork inherent in that game), but they are hardly a spring chicken. Like Paul Barnett said, the market changes as time passes.

Personally, I think that it would be an excellent idea to put something like this as an optional side-quest, similar to the monster arenas in the various final fantasy games. You often have challenges that are tougher than anything else in the game, and usually by the time your characters are strong enough to defeat them, any sort of loot reward is mostly pointless. So instead, you give special bragging rights rewards, like a special title, a special visual effect, a special mount, or some other cool thing. Absolute Virtue does drop items, and those items can lead to some of the most powerful items in the FFXI game. However, that in and of itself doesn't necessarily mean quite as much -- the belt it drops (Ninurta's Sash) has +6% to haste (which is the big deal). There are several questable belt rewards that give +4% to haste, and 2% is really not a huge difference in performance, especially given how slow-paced the game is.

The real benefit of beating Absolute Virtue would just be the bragging rights to say 'Yes, we beat it'.

So what do you think? Is there any value in designing an encounter that can't be beat for years?