I only use my throat to increase the pitch, as the pitch goes up you notice more throat sound.
however I use my diaphragm to actually bring the air to a scream rather then just talking and pinching your throat.
all of those are actually very old too, i've increased my pitch and tone to a better quality since then.
the err... growl, was when I first learned how to growl. I can do at least 4 or so different growl types now (mimiced after vocallists).
but yeah, I'm not saying that you personally suck or you are'nt going to get anywhere with what you're doing, but listen to bands, none of them use the tecnique that you're using, A because it does'nt sound very good, and B because it damages the throat.
once you can master the diaphragm, just tweak with air/throat/tongue placement to find different tones and abilities.
edit: And I just realised how old those videos must be, considering my hair was at my ears in those videos, and I just recently got my hair cut because it was past my shoulders.