Originally Posted by 2ndGen

Not necessarily in the case of a drivetrain. Better quality materials and features "can" possibly weigh less. A good example is how the Dura Ace Rear Derailleur can supposedly survive a crash because of it's build quality while being lighter.

BSM has put together what I believe to be one of the most detailed explanations of what goes into Ultegra & Dura Ace:

http://www.bikesportmichigan.com/fea...-ultegra.shtml

A 105 VS Ultegra exchange...

http://www.beginnertriathlete.com/di...187662&posts=7

Ultegra is much closer to Dura Ace than it is to 105.