This post contains so many errors it's almost funny. NO song on the album is in DADFAD. Here's the breakdown:
Ghost of Perdition, Baying of the Hounds, Reverie/Harlequin Forest, The Grand Conjuration, Isolation Years - DADFAE
Atonement - ????? (The guitar is simple enough on this song there's no way to tell, but it never goes lower than E so I'd assume standard)
Hours of Weatlh, Beneath the Mire - EADGBE (standard)
There's a VERY accurate tab of Beneath the Mire on powertabs.net, the only problem I have with it is the very first riff sounds kind of weird. But yeah, if you listen to the song, there's never a guitar note under E (and there are a TON of low Es in almost every riff) and there are tons of riffs that would be hard to finger if it had a dropped D, not to mention there are a lot of fourth chords that are annoying to finger in dropped tunings, and none of the acoustic stuff has fingerings that would make sense in an open tuning. Mikael said something about the number of songs in standard way back in the day that backs up the idea of Atonement/Hours of Wealth/Beneath the Mire being in standard too.