Originally Posted by
Jeff Wills
It's not just "down". Cantilever posts on older touring bikes were also closer together laterally. This leads to compatibility issues with newer cantilever and V-brakes because the brake pads are moving in a different arc than older brakes. This can be worked around by a knowledgeable mechanic but can be very frustrating for those who assume that the switch is straightforward.
That would only be more reason to have a framebuilder - or a good mechanic with a torch - move the posts.
Mount spacing has never been ironclad and there has always been a range that works for any particular brake. No one is going to light torch without a clear idea where they are headed.