Ignorant question about sharpening and the 7D!

And I truly claim very little in the way of knowledge of cameras or photography in general, but I'll ask this question anyway as it has been plaguing me for some time now.

Why is it that we have to sharpen in post? Is this just the 7D or is this the normal course of action with all cameras? If you shoot from a tripod and have your shutter speed up do you need to sharpen? Is this just an inherent quality or non quality in cameras that you must do some sharpening? It just seems to me that if you pay $1700 for a camera, and provided you are using it properly, shouldn't you be getting some tack sharp shots without sharpening in post? And also providing you have a good lens?

I know there is a lot I don't understand, but this particular issue seems very strange to me.