Isn't that the main ways you die in real life too? Barring old age, of course. In reality, most premature deaths are, in one way or another, caused by:
a) Suffocation (including drowning)
b) Bleeding (internally too)
c) Brain trauma (or beheading, if you want)
d) Infections (and disease)
And all of these can happen in DF. That being said, i am somewhat irked at the low killing power of blunt weapons, as well as the general ineffectiveness of bruising internal organs. If you took a hammer strike to the liver in real life, you'd collapse in pain and suffer severe internal bleeding. In DF, you go "ow" and chop the hammerman's head off, possibly with some pain involved, but nothing crippling. Likewise with kidneys; they supposedly hurt like all hell to get hit in, and a ruptured kidney bleeds A LOT. In DF, my adventurer easily survived getting stabbed in the kidney by a spear.
In other words, a severe blunt impact should rupture internal organs, not just bruise them. Not always, naturally, but it should happen sometimes. Also, organ damage should probably be a tad more severe, and skulls should break less easily, if it were to be totally realistic. Otherwise i'm mostly happy with the combat. ESPECIALLY how you have to deal with large creatures in a more realistic manner. The classic i-stab-your-toe HP-draining combat bugs me, so being charged and smashed by them in DF is almost refreshing. Almost.