Ages ago, blogger and one-hit-webcomic-wonder Shamus Young wrote about an idea he called "Self-Balancing Gameplay". The idea of this was that in any "RPG" style game, the fact that your character gained experience and equipment, allowing you to become more powerful and better at killing things effectively allowed players to choose their own difficulty setting. A hardcore powergamer will blitz through the start of the game until they get to the area where the monsters are tough enough to challenge them, while a meandering casual will dither around grinding rabbits until they're tough enough to take on the big bad world.
It's a decent enough theory, but it falls down in practice because gamers don't actually think that way. In practice the hardcore powergamers will squeeze every last drop of loot and experience out of the starting area, before going on to do the same for the next area, and the next, and the next. The power-gamer will, at every stage, make things easier on himself by optimising his use of resources. The casual gamer, on the other hand, will get bored of killing goblins after five minutes and see what's over the next hill, at which point they will get their face chewed off by Enraged Goblins and Goblin Savages.
It leads to a peculiar paradox: hardcore players do things the easy way, casual players do things the hard way.
Never is this more evident than in WoW.
Read any WoW levelling guide and it will say the same things: avoid instances unless you've got a regular group, do the green quests because they'll go much faster and net you nearly as much XP.
This was not how I levelled any of my characters (which might explain why my DK - my highest level toon by a long way - is only level 78). By the time the quests I have left in a location have gone green, I am *bored* with that location. I want to go and see the next bit. So I'll always be doing yellow or orange quests, for which I will be low level and undergeared, while the serious players blitz through the content having a much, much easier time of it. My first PC (on a now-deleted account) was a Forsaken rogue who spent *forever* getting slaughtered in the Tirisfal pumpkin patch at level four, because I couldn't be arsed to scour Deathknell for leftover supplies, and wanted to take the filthy living down a peg or two.
This is also the reason that balancing endgame is so impossible. A common complaint amongst serious raiders is that you can stumble into Naxx in quest greens, and still have a chance of beating the place.
The perception of endgame is that there are two camps of players: the "hardcore" players, who want a serious challenge that takes time and effort (0r "have no lives" according to the casuals) and the "casual" players who just want to see cool content (or "get free epics" according to the hardcores).
I can't speak for the Hardcores. I'm not one by any stretch of the imagination. I can't speak for casuals either, because we're a varied bunch. I can talk for myself, and this is what I'll say:
I want a challenge. I want a dungeon that requires everybody involved to pay attention, use their abilities sensibly, and have a strategy. I want to use CC and interrupts and kill the healers first, instead of just AoEing everything into the ground.
On the other hand, I don't want to have to run the same dungeon ten times just so I can get the right gear to do the next bit of content. I want to be able to go into Naxx in quest greens, because I want my ability to succeed at the game to be based on how well I play the game, not on whether the RNG gave me the right loot on my last dungeon run.
But of course, if a dungeon or raid is tuned so it's a challenge for me, it's going to be trivial for "hardcore" players, who will have optimised at every stage, and wouldn't dream of going into a new area with anything less than the best gear available from the old one.
The problem is exascerbated by the fact that the standard reward model in RPGs is loot which makes your character more powerful which, in turn, makes the game easier. This pretty much inverts Young's idea of "Self-Balancing Gameplay" and turns it into Self-Unbalancing Gameplay. More "serious" players will not only tend to play with greater skill but they will *also* have better stuff - meaning that the "Self-Balancing" mechanism of gearing actually starts to work the other way.
Blizzard's response to this is to add "hard modes" to their instances, but this isn't a solution either, because hardcore players won't just do the hard modes, they'll do the easy modes, then the heroics, then the normal hard modes then the heroic hard modes, moving step by step up the gear ladder so they never face a proper challenge because doing it any other way to a "hardcore" player would be completely illogical (unless you were racing for a world first, which some people did, only to find their achievements were removed because they did it "wrong").
If it was just a question of "people who want it easy" versus "people who want a challenge" the whole thing would be straightforward - you have two dungeon settings, one noticably more difficult than the other. The problem is that what you actually have is two sets of people, both of whom want a challenge, but who are willing to do vastly different levels of preparation before facing that challenge.
Anyway, I need to finish the last couple of levels to 80, so I can blunder into Naxx in my quest greens...