This is in response to this post on Player vs. Developer. Normally I'd just add a comment, but I'm having trouble phrasing my response and I'd rather not clutter his blog with my own rambling responses which can end up longer than the original. So, go read his post first.
Gear is the breaker of learning curves. If gear can make content easier, it can also sometimes break learning curves. Imagine a fight that requires a certain DPS. Bad, undergeared DPS won't be able to do it. But what about bad, overgeared DPS? The encounter that should be forcing them to get better is just causing them to get better gear elsewhere and return when the fight is trivial.
There are some fights that care less about gear. Being sufficiently overgeared could conceivably overcome the zombie healing on Gluth. A fight that completely ignores gear is the last boss of the Oculus. I don't think it's a coincidence that this fight has given me so much trouble. It can't be outgeared so people are forced to learn, and that's a painful process that we tend to avoid.
Fights like this are rare, and more importantly, never truly required. They can be skipped, avoided by some means. This is nice for subscription numbers because it never creates a barrier that could cause people to give up in frustration and stop giving Blizzard money. However for the playerbase it means that only people who actively try to learn will actually learn.
Instances are an example of content that has a learning curve, but it can be skipped by two means: overgeared and other players picking up the slack. Often others pick up the slack by being overgeared themselves. Why learn when you can just surround yourself with better players? Given enough time you will get enough gear to not need to learn.
The materialism of players isn't necessarily bad, but it does mean that those who do not help one to get gear (people who are learning) are pushed out of the way. There is no gear reward for teaching people. Eventually they may learn and help in getting gear, but why not save time and just get someone that already knows what to do?
WoW is anonymous, and not just due to the RL->virtual life conversion. Even on a single server, the population is large enough that slighting someone now isn't likely to have significant negative consequences, perhaps ever. Ninja now, pay... never. Kick a noob and he's not likely to come back around and be the only healer you can find. A smaller, closer-knit community would be more likely to help each other because they'd see that they need each other. In the vast sea of thousands of people per server with name changes and server transfers, it's hard for negative actions towards another player to ever catch up.
TL;DR: Why learn when you can overgear? Why teach when you can replace?
To fix this, WoW would have to have a lot more fights like Oculus, but is it really worth it? Truly challenging fights like that would drive away a lot of the playerbase. They would also become repetitive too fast. Current content may be beaten by skill early on, but eventually gear carries the raid and they can breeze through the boring stuff. Imagine if every fight was exactly as hard the 1st and 100th time. That would be unimaginably frustrating.