I don't think I'm being unreasonable here. In a closed system this should be doable.
edit: one of the reasons I think this is because we are supposed to be engineers, and other engineering disciplines do it (and their disciplines involve computes too). Consider jets and boats.
He may be an engineer, whatever that means, but still: the average joe in that position will not spend a single second on thinking if he expects the solution he's buying to work for a reasonable lifespan. He's been thrown in a project, that's all. If you force him to state a requirement on the expected lifespan, he will surely say 'Well, as long as possible seems good to me'.
Disclaimer: statistics applies here, of course some people will care, but I'm speaking about the 80%, if not more.