Hi CS,
I agree with what you say in principle CS.
However, in practice, I think that "curry powder" is often prescribed in such relatively small quantities that it is likely to have only a relatively small effect on the final outcome. That's why, in my recipes, I say that "any decent one will do".
Nevertheless, I agree that it would be more precise to either define the brand of curry powder (or garam masala) being used or, better still, to define the individual ingredients used to make it. This can sometimes present a problem in that some hard-to-find ingredients are then specified (Knorr Vegetable Bouillon Catering Paste anyone?)......but at least the options are then open I suppose.
In my experience, BIRs also use commercial blends of whole spices, masalas and pastes and generally do not know what they comprise of!

Regards,