[espadrine]

I agree that there are some robotic designs that unnecessarily mimic human limbs. I have in mind heads, and feet (instead of wheels).

A hand however, is useful because so many manufactured objects have been constructed for their purpose.

[swiftcoder]

Feet are used for roughly the same reason a human-like hand is preferable - human-designed spaces tend to not be perfectly compatible with wheeled locomotion.

The ability to negotiate stairs is table stakes for a household robot. It's already a pain when one's Roomba-like is defeated by a small ledge...