You are right. If the hand is doing a specific task, better morphologies are likely. But that's not always desirable. The canonical example is of course the household. I don't want X robots, I want 1. And I don't want to change anything. Robot hand!

Not to mention that the world is very widely designed to be manipulated by hands: doorknobs, handles, container sizes. A unique door opening appendage isn't going to do much good around your house.