I don't think practical cryptographers ignore the difference between computations and interactions—there are different threat models and they are carefully stud

I don't think practical cryptographers ignore the difference between computations and interactions—there are different threat models and they are carefully studied. Part of the problem might be that a system designed to be safe against 2^32 interactions is deployed in a place where the system is vulnerable to attacks on the order of 2^32 computations. The problem I think the author is highlighting is that the mistake risk distribution is hard to understand. Some kinds of off by one errors may cause relatively small reductions in security margins. Some kinds may cause complete loss of system integrity. It's hard to distinguish between the two without extensive testing and expertise. Furthermore, the kind of user who would never tell you about your error is exactly the kind who will find it. Finally, loss of your security infrastructure is unlikely to cause just small visual discomfort to your users—it's likely to hurt them materially.