I think there a number of different reasons why people rip through content so fast. Dungeons do have a timer and if you get stuck on a section for a long period of time, you at least have leaway. (highly unlikely though) . People want to dungeon over with, so they can get back to the MSQ. I know I am always desperate for the next bunch of cut scenes and storylines to be launched. Finally, people just have the World Of Warcraft mentality, where you want to rush as fast as possible, so you can score a world first or server first.

Outside of dungeons, I typically take my time, so I can soak as much in as possible each time I log in. (due to spinal damage, I can only sit at my desk for limited amounts of time, which forces me to log on and off several times a day.