It seems that nowadays ppl have forgotten all about real doom metal. what is there in common dude? how can you compare lets say Morbid Angel with Solitude Aeturnus. I understand that the term Death-doom metal is oftenly used, but i guess it all is about the vocals and the history of the band.
My dying bride for instance started as a death metal act but has ended up to what we call doom death. where is the death elements of MDB's last lps though? if there are any they are minimal.
Doom the way i have learned it throughout time consists of bands like Candlemass, Solitude Aeturnus, Sorcerer (though a bit more epic), Solstice, Last Chapter etc.
Death can be defined by acts like DEATH (the optimum definition), Morbid Angel, Carcass, Bolt Thrower etc.
The combination of the death growls and in some parts (few) the riffs with the heavy, pessimistic atmosphere, slow riffing could be the definition of what ppl call doom-death metal.
i dunno.

that is what my thoughts are for now...