As far as I understand it, the node is more useful for car routing, since it marks the exact point on the road where the intersection crosses, while the way is more useful for pedestrian routing, where the actual path to be traveled is more relevant. I agree that it seems redundant, but for all I know, car routers might totally ignore any pedestrian footways, which would prevent them from filling in the crossing data on the fly.

Does that really matter if there are proper systems to deal with the pollution?