+1.While I do agree with this, I would also say that sometimes it's far easier to just downtune a 4 string.
Especially in heavy music where the riff constantly goes back to the open D, it would be a royal pain to have to go back to the 3rd fret of the B string every other note.
For this specific case, the detuner really makes more sense... where it's handy to be able to pedal a low D maybe while you do other stuff. If I were in a different kind of band that did that kinda' thing a lot more, I'm sure I'd feel differently about detuners.
