There are many applications of humanoid robots when they become good and cheap. Right now they are neither, but DARPA is funding people to work on this.

Cheap, good humanoid robots will fill the slave niche in society, without the ethical problems (at least in terms of the slaves themselves - it might not be good for us to be slave owners, but we'll see how that pans out). Who said the researchers are or should be thinking about only this century?

By the way, a mobile gun platform on wheels is not going to be great in built-up areas. This is why we don't have combat soldiers fighting in powered wheelchairs, and why Daleks suck.