Yeah, now that you mention it, going from 6 or 7 speed to 9 or 10 probably requires chainrings as well, to accommodate the narrower chain. I don't know that for sure, nor do I know whether you could slap new chainrings onto a vintage crankset or whether that would need to be replaced too.

The limiting factor there is the number of speeds on the rear. If you had separate shifters and brakes on a 9 speed bike you could replace them with brifters alone.