为什么要限制密码的长度？

I've just signed up to a site to purchase some goods, and when I tried to enter my (reasonably secure) password I was informed it was too long, and that I should enter a password between 5 & 10 characters! What is the point in that? Who makes decisions like this? Surely the ideal password would be a really long and complicated one? Why do people insist on trying to restrict what types of passwords you can use?I've just signed up to a site to purchase some