Why should app developers have the power by default? It sounds to me like you're arguing for that just because that happens to be what you have trouble with. But I'm sure we can find plenty of other people where having the default be the other way would work better.

Your actual problem is that your users can't change even the most basic settings, and you're not in a position to change it for them. I'm sure autocomplete isn't the first nor the last symptom you'll have due to this problem. Good defaults are important, but good defaults are about more than what works for shared desktops in schools with clueless IT people.