No-one is saying that adding AIF checking is a bad idea (although I think some of the RO5 developers have stated that Castle looked at it and decided that breaking an even larger amount of legacy software was a bad idea).
The problem is that there was no warning of this to developers. Claiming that it was in an old (and largely ignored) Acorn apps note from 1996 isn't enough: ROL should have told developers about this 6 months to a year ago, in the sense of "This will happen, in mid 2006", and then it could have been prepared for. As far as I know, not even Select subscribers were given the heads up:
there certainly wasn't a mention of it on the Select mailing list.