There's a huge difference in what is playable, the lowest note matters less than the relations between the strings in determining the sound of a song. For example, it just isn't feasible to play some of the riffs from ghost reveries in a drop D or standard D tuning, because of the notes in the arpeggios they let ring out. To play the same thing in D standard would be extremely difficult to finger and wouldn't ring, and they probably never would have come up with the note sequence if they had been playing in a tuning that wasn't encouraging of those particular arpeggios. Even simple Drop D has similar issues, like it's absolutely not possible to play Demon of the Fall or Blackwater Park smoothly in a guitar that's in D-standard tuning, if you played guitar yourself you'd understand but it's hard to explain.
Well, it´s an opinion! Cheers
