It takes a few seconds to kill a pack. The pack will give high experience, with rested most likely over half of what the random dungeon reward is. Even running random dungeons one after another, you won't be getting higher experience by skipping packs.
Experience is what 99% of the people in the instance are there for. Gear is made useless in a few levels by access to the next expansion's content. Most people have heirlooms anyway, and if you don't, skipping content shouldn't be your priority.
Tons of awesome fast experience has been lost this way. Pointless Wrath of the Lich King mentality remnant.