I cannot agree with their thinking here. If they presented the information, and let people decide, fine. But if a bug will give predictable errors, speak up at once, or be prepared to pay forever after. The alternative to this is to have oodles of checks and backups. This may be very difficult to do.
Humans can carry out checks faster than computations, but modern computers are much slower at it.
It would probably be cheaper to eliminate all floating division, with all the programming that involves. I don't know. I don't know enough about the particulars in this case. For each user who IS affected, there may be even hundreds who do not know if they are affected. If it was announced promptly, those users who could have put in check procedures would have had an opportunity to do so.