I was under the impression that the trend for detuning in metal was about expectation of a heavier and more gritty, growling sound. It got to the point where bands were progressively going lower because older music started sounding comparatively pipey and flamboyant. It wasn't about accommodating vocalists, although it can definitely be used that way and sometimes works better that way.
As much as people like to celebrate Maiden for not being sellouts, I'd rather hear them evolve and do justice to their own compositions rather than take a shot at how it was meant to be in the 80s and not get there.
Again, though, this is typical Maiden PR as much as anything