The other night, my World of Warcraft guild and I made our first exploration into the frigid halls of Icecrown Citadel, the final (and most difficult) raid dungeon in Wrath of the Lich King. We're hardly top-tier raiders, so we spent the night learning the fight against the dungeon's first boss, Lord Marrowgar - and, after a couple of near victories, left empty-handed to try again next time.
One of Marrowgar's abilities is to throw bone needles at three random members of the raid, impaling them and rendering them unable to act until the needles are destroyed by their comrades. It's normally not a problem unless he hits one of the raid's healers. The giant skeletal guardian is dealing consistently heavy damage to all three tanks, and an incapacitated tank healer means that someone else needs to pick up the slack or everybody dies. After one particular wipe, our raid leader pointed out that it was just something we were going to have to get used to, since it wasn't like the boss would adjust his abilities or damage if one of the healers had been one of his targets.
The other game I've been spending a ton of time playing recently is Valve's Left 4 Dead 2, where the AI Director is programmed to do exactly that - adjust the experience so that the players always stand a fighting chance against a challenge. If the Survivors are broken and bleeding, the Director conjures health and ammo; if they're fighting their way through the Infected without a problem, the Director spawns a trio of minibosses. The end result is a game with very effective crescendos of chaos, but one that almost always seems (somehow) manageable.
This is actually not a concept unique to Left 4 Dead; as Anthony Burch wrote back in Issue 195 of The Escapist, developers use very tightly controlled behind-the-scenes tech in order to evoke a specific emotional reaction in the player, and to make them feel like they triumphed over impossible odds. In Half-Life 2 Episode 2, you'll get overrun by the Striders no matter what - but still pull through in the end - and in Metal Gear Solid 4, you'll make it to the end of the game's climax broken and battered, but in one piece. Maybe it's a bit of developer trickery, but it's a damn good one.
So why couldn't we see it in a high-end raid in a game like World of Warcraft?