Drop tuning a semitone certainly helps bending – can you imagine playing the opening guitar solo of Estranged at normal pitch? I think it's a two or two-and-a-half tone bend
My sister (who has a music degree) told me once that A = 440 Hz was only standardised during the 20th century and that prior to that it was mostly standardised around a frequency for middle C (which I can't remember) that equates to the modern A=440 drop-tuned a semitone. So really, drop-tuning is going back to an earlier time. Of course, I think America now tends towards A = 442 as it sounds brighter.
I agree that it tends to sound more mellow or "minor".
