This is an interesting debate; I'm not sure there *is* a clear definition of curry powder really. I guess it comes down to what ingredients it is intended to be a substitute for, which varies quite significantly by brand and style according to the ingredients lists I've been looking at.
Just to muddy the waters a bit further, certain ingredients can end up being added more than once is some recipes (including mine!). I use cumin at the initial tempering stage, as well as using it in my garam masala. Coriander is another one, with the seeds going into the masala and the leaves/stalks going in at the end of the cook.
I always thought of curry powder vaguely as a balancing ingredient, though that doesn't quite fit either as some don't include ginger and others don't include garlic.
The only conclusion I am prepared to draw is that it is a variable mix powder that isn't a good substitute for garam masala but can be a good alternative to turmeric on its own.