Yeah it is odd how most of the Quake gibs are humanoid, but I imagine ID ran out of time and hit model limits (255 per map). I originally created the extra gibs for weapons but I extended it to body part as well. I cut most of the creature parts at the leg and arm bone joints. The stumps are painted with extra gore and blood and the edges are made to look uneven. (probably not easy to see in the screenshot). Unique gibs are fun to see when enemies explode up close while doing a stealth backstab. The real problem is that all of the original head models are 25-50% too larger (id design so they can be seen) and that does look odd!
My favourite gibs are certainly the weapons, I even repainted some of the original Quake monster weapons, but got the texture resolution wrong! doh!

Well he was evil, but he did build a lot of roads. - Gogglor