3D apps always use all cores. Modo, Maya, Realflow, and Houdini all use all of my cores.
that's not true.. 3d apps only use all cores when/if they have a render engine going..
for instance, autocad uses a single core for most (by far) of the workload.. when it does use all cores, it's actually mental ray which is using those cores and not base autocad..
sketchup has no render engine (per se) and it never runs on more than one core (in fact, it's still a 32bit app because there's no gains/need for 64 bit until rendering comes into play)