Is Celtic Frost even considered Death Metal? I've always considered them Extreme Metal, because they don't lock into one genre. They've always had a mix of Thrash, Doom, Black, and in SOME cases, an early Death Metal sound, minus the vocals.
Stuff sounds the way it does because the producer and where it was recorded. If you wanted to get down to why distorted guitar tones vary on Death Metal albums. It's kinda a dumb thread.