One of the interesting things about Skywall, at least compared to the other servers I have been on, is that the endgame guilds do not have spec requirements. They also have very low gear requirements. Additionally very few of them have extensive loot restrictions. The majority that I've looked at have open loot, but frown on passing on set pieces, or will force people to take them.
This is very different than many of my previous servers. Off-specs, like feral druids or shadow priests, are disdained, and many guilds require people to have a certain spec. Additionally, high end guilds tended to have very high gear requirements, especially when it came to resistances. Finally, class restrictions on gear were the norm, especially when it comes to dps vs hybrid gear.
So why is Skywall different? I think it's mostly due to the influence of the lead guild on the server. The lead guild, or the guild that has advanced the most in the end game, is a guild called Rebirth. Rebirth believes very strongly in the viability of off-specs in raiding. Additionally, their gear requirements are pretty low, though they are very discriminating in actually guilding people after trials. And they don't seem to have loot restrictions.
The lead guild, in many ways, sets the tone for the server. A classical economist might say that this is because of competition. A lower guild cannot set higher requirements than the lead guild, because that would drive better players towards the lead guild.
I'm not sure that is quite right. A lot of guilds have spec/gear/loot restrictions because the guild believes that it is necessary for progression. They get the idea that it is necessary from the lead guild. An appeal to authority, as it were. If the lead guild requires specs, than we probably should as well. People try to imitate people who are successful.
On Skywall though, Rebirth serves as a counter-example. Guilds that want to be successful on Skywall try to imitate Rebirth, and that means that they tend to avoid spec/gear/loot restrictions.
One interesting area where lower guilds do not follow the lead guild is loot systems. The fact that a lead guild uses a specific loot system doesn't seem to influence the lower guilds. Each guild seems to come up with it's own system, and what the other guilds do has less impact. Every server I have been on displays this pattern.
My guess is that the loot system is evaluated on fairness as well as progression, and people feel more able to evaluate fairness than progression. If you ask, "Does having off-specs help us to progress?", you can point to the lead guild for evidence. But if you ask, "Is this loot system fair?", the answer hinges much more on the internal structure of the loot system than what the lead guild does.
In conclusion, the lead guild has a lot of influence on progression-related matters. If a question relates to progression, very often a guild's answer will be the same as the lead guild's answer. However, if the question moves away from progression, the lead guild's influence lessens dramatically.