How in the world is slipknot considered death metal?

They do not talk about the subject of death, occultism, philosophy,
and social commentary (they talk about failed love and complain that
the world sucks and other teen angst lyrics, " people = shit" dark
lyrics? far from it). They shout and dont growl (hence death growl),
and they rap (specially the first album like spit it out and eyeless).
and they switch from screaming to singing to rapping, something that
death metal bands dont do. And how in the world is snuff and dead
memories death metal? snuff sounds like some emo song, no death metal
band or even any metal band would do that (sellouts). plus they take
the whole satanism thing too seriously, and sounds embarrasing
,seriously "If your 555 im 666''? and death metal is supposed to be
anti commercial, they get their album sales from image, they even
change masks for every album, shows how commercial they are. there are
bands way heavier than them and they arent even considered death metal
such as lamb of god, theyre not good but theyre heavier than slipknot,
and not even death metal or considered it.

This is an example of death metal:
http://www.youtube.com/watch?v=t_WGRqtI9z4

These bands are heavier than slipknot and arent death metal:

http://www.youtube.com/watch?v=0Ks1S5e4GOc

http://www.youtube.com/watch?v=hI8lIhFd3AQ

why do people, especially maggots think theyre the most brutal death
metal band ever when theyre not death metal? theyre %100 Nu metal, i
should know i used to listen to some nu metal (disturbed, SOAD)
lol yeah i heard my lead guitarist say theyre death metal but i had to
lecture him when i was trying to get him into metal
and i hear lots of people at school say that, especially their fans