Originally Posted by bikingshearer

Absolutely not. At least not stronger in terms of the type of forces that kill spokes.

Take it from Jobst Brandt, who has forgotten more about spoked bicycle wheels than most of us will ever know:

"[T]he most valuable contribution of swaging [i.e., double-butting] is that the peak stresses are absorbed in the straight midsection rather than concentrated in the threads and elbow, thereby substantially reducing fatigue failures. Swaged spokes act like strain screws commonly used in high-performance machinery."

J. Brandt, The Bicycle Wheel (3rd ed.1993) at 47. In other words, in butted spokes as compared to straight-gauge spokes, more stress gets taken up in the mid-section, where breakage almost never occurs, and less stress is left to be absorbed by the elbow (where most breakage occurs) and the threads (the next-most likely place for failure, although rare compared to the elbow).

It may be harder to take a straight-gauge spoke in your hand and bend it than with a DB spoke, but that isn't the kind of force you are dealing with in a bicycle wheel. Simply put, all else being equal, a 14/15 gauge DB spoked wheel is stronger and will last longer than a 14 gauge straight gauge spoked wheel.