Every class has combinations of discs / abilities that pair well with other classes' stuff. Some do nearly the same thing, so hitting that particular disc when another buff with a similar effect is going won't net you the best overall effect. I think that where some of these guilds excel is knowing what works well with what, and micromanaging their burns better. For example, instead of just saying "OK hit your big discs now", the raid leader might say "OK everybody hit your first wave of discs" which have been set up previously to give the greatest possible benefit.
On a short burn where you really only have time for 1 or 2 discs, it's not as big of a deal, but on fights that get a bit longer, it can make a difference.
Also, DPS doesn't necessarily scale well from event to event for comparisons. Mobs have weaknesses to various spell and weapon types. Tyranot parses will be inflated, especially if the guild has a lot of rogues and smart zerkers, because he has a weakness to pierce damage. Instead of aiming for other guilds' goals, I think you're best off looking at what you guys are doing, and seeing trying to find room for improvement.
