Not alternate tunings, not one instrument out of tune, but the whole song recorded slightly off standard tuning? I was listening to Metallica's Ride The Lightning album in the car today and remembered when I used to play along to the whole album on guitar and when 'For Whom the Bell Tolls' came on it would always sound wrong cos the original is slightly off tune. Same goes for Radiohead's 'No Surprises', it's not quite in tune with the rest of the album.
Why?? Conscious decision or a mistake made in mixing with the tape speed?