One of the most important features in WoW is actually one that most of us who have been playing the game for a while don't even think about. In PVE, the way in which you get the majority of your gear, and indeed, the only way to get the very best gear, is to kill bosses and hope that A: the piece from their loot table that you want drops and B: that another player does not win the roll for it.
This has been the case for the game's entire history, but I am not so sure that it makes the game better.
RNGs control the game. Everything has a bit of randomness built into the system - whether your attack hits or not, if a talent proc goes off, or whether that bear you just killed dropped one of the pelts you need for your quest. When the RNG gods favor you, it's great. The one time I pugged ICC on my Horde Shaman, I walked away with five pieces of gear. When they do not favor you, it's awful. I similarly spent an entire month running heroic Forge of Souls before I got its pair of tanking boots - one run, every single day.
While one could cite the random boss loot as a way to extend the lifetime of content, it's also possible that it could be shortening the lifetime of the content - in those cases where people get what they want early on, they will feel held back if their guild is not moving on or if there is nothing ahead of them.
Blizzard has attempted to make the loot drama over drops in LFR less severe by giving everyone their own, individual roll - you either get something your spec can use or you don't. This certainly does a great deal to help with interpersonal loot drama ("You shouldn't get that staff! I did way more dps!" - a comment I despise because often it is coming from someone far better geared, who thus, of course, needs the piece less.)
But the frustration of the random loot drop is still there. Mind you, it's nowhere near as bad as it is in Diablo, where not only is there no guarantee of bosses dropping high-quality loot after the first difficulty, but also every single piece of gear has randomized (and thus, probably pretty bad) stats.
Here's what I like about the WoW loot system: The table of loot a boss has can have some character. Even if the pieces of armor simply look like tier gear, the names can have a degree of flavor. It makes a lot of sense that the axe off of Marrowgar (25) looks like the axe that he uses. It also means that you know where to go and who to fight when you want that specific item.
But beyond that, it's mainly a source of frustration.
In Burning Crusade, Badges of Justice were introduced to give long-term rewards for people who wanted to focus on heroics. Later, they decided to make raid bosses drop these, transforming them into a means to smooth out the ill effects of RNG. By 2.4, you could actually get some very high-quality weapons for Badges. This pattern was continued and refined through Wrath and Cataclysm, with Wrath introducing tiered currencies, and then in 3.2 simplifying things by making all non-cutting edge content drop the next best currency. Cataclysm merely formalized things by creating Justice and Valor Points, which would always be the 2nd best and the best PvE currency, respectively.
Blizzard claims that they felt that these currencies were allowed to run a little to rampant in Wrath and Cataclysm, overtaking the importance of boss drops.
My reply is: so? Yes, people will argue that the RNG of loot drops is what makes killing a boss exciting, but after killing a boss for the 20th time and still not seeing that sword you want, I don't think it's really excitement that you're describing.
On one hand, experimentally I'd like to see a game like WoW in which every single piece of gear was currency-based, and not random drops. You'd pick up what you needed, paying for it with the VP you got from fighting bosses. Harder bosses and later tiers would give more currency, so you'd still be encouraged to push yourself.
This being WoW, and having a history, however, means that I would not do something so radical. Instead, as in most things, my solution would be a hybrid system.
We like the personality of having pieces of gear dropped from particular bosses. You should not be able to get, say, the Claws of Shek'zeer without having killed her. But we would still have a way to combat RNG:
Items off a boss (perhaps only particular ones, if normal VP rewards cover the slots filled by certain drops) become unlocked to buy with Valor points when you defeat a boss (or perhaps after you beat it a certain number of times, like 4 or 5.) The price for these items in VP would be quite high - higher than the current max price of 2250. They would still have a chance to drop off the boss, but if there was that one piece that you really needed, you had a way around the RNG gods that wasn't just praying to them again (which is what the Elder Charm of Good Fortune is.)
So you would still likely be getting most of your gear through loot drops. The difference is that while you would be very happy to see your piece dropping, you would not be discouraged if you saw a string of kills without the drop.
The major point of all of this is that it makes things fair. Anyone who manages to down a boss is going to have equal chances at getting what they want from it. With a system like this, they will eventually get it. And at something like 3k VP a pop, it's not like people are just going to buy out all the gear they need out of the raid in a month.