Just In Case

So you send a letter (or important documents) from the post office. And for an extra fee, they will offer delivery confirmation that your package got to its recipient. Is it just me, or does this seem silly? Is the postage paid on the letter not already a fee charged to ensure proper delivery? So ... aren't they simply trying to get me to pay them extra to do their job right? After all, if they did their work properly in the first place, delivery confirmation should be a redundant service instead of an afterthought service to add peace of mind in case they don't!