Or I could think of it as gambling that enough other people either 1) are lucky, 2) don't bother with the return ("I don't really need it/want another.") or 3) forget about the return.

But, I don't think of it in terms of how much money I "save" by breaking stuff.

I pay the extra cost and try to be careful. What I get back is Less Worry. If the thingy breaks down, I get a new thingy. That's worth money to me.

The alternative is to handle the risk myself, and saving the 10%s into a "surprise expense account" to use when things break down. I'm convinced I don't have the discipline for that - both managing it and not using the money for other expenses.