Why use signed integers?

I've noticed that, in quite a few MMORPGs, the stackable item/money cap is (2^31)-1, or 2,147,483,647.

But why use a signed integer? Do you really need negative amounts of items?

Why not use unsigned integers and then have the cap be (2^32)-1?

>>29
the number of characters
What does this have to do with anything? When checking for EOF, programs loop through each individual character. That's what it's for.