Originally Posted by
Monster Pete
With a double chainring, you only have two basic front derailleur positions. Since to shift a double you pretty much just pull it until it stops, there's no real necessity to have an adjuster. They're only really needed when you have indexing, in order to line up the shifter positions with the chainrings.
Shimano's left-hand double brifters have a third position for trimming, would the barrel adjuster not be useful for adjusting exactly where the trim position puts the derailleur?