That's just it, Steam are supposed to be limiting automatic updates to off-peak hours more than usual, not sure if that means they are also throttling the actual downloads or not.
Also if Steam can hit 70MB, I could easily max out Gigabit by the Xbox One downloading an update at the same time and watching Netflix 4K on my TV. A scenario I would absolutely have done today, had I not deliberately chosen to watch content off Plex instead to avoid said scenario.
Heck, there are times when Windows is updating, Steam is updating and I want to play GTA or something off UPlay that also wants to update. The chance of that happening or being a problem if does, is dramatically reduced with Gigabit.