I can't play guitar for shit, but I'm wondering if Drop D, or any other tuning for that matter, would be in any way similar to the F-attachment that you have on higher-end model trombones. Bear with me here, this is the only instrument I really know:
On a "triggered" trombone, you basically have a special piping assembly that lets the musician press a trigger to "cheat" and play certain notes without having to move the slide aaaaall the way out. This can either make the horn player in question a lazy sack of crap that uses the trigger for EVERTYHING, or in the hands of someone with a certain degree of skill it can add a significantly greater range of notes, and decrease the physical limitations of the instrument, making the artists' repertoire that much greater. Long story short, it can be either a tool or a crutch depending on how you use it.
(and with that, I officially make my most pathetically nerdy post in my short life on these forums)
Wouldn't the drop tuning for a guitar be much the same?