Xbox One can support up to eight controllers connected to the system simultaneously. Multitaps everywhere were rendered somehow even more obsolete thanks to Microsoft's shop listing (opens in new tab) for the controller (via VideoGamer), which otherwise lists several previously confirmed features for the updated peripheral.
Xbox 360 only supported four controllers while PS3 could link up with seven. SCE President of Worldwide Studios Shuhei Yoshida confirmed in a tweet that PS4 can only connect with four controllers at once, but he didn't say why the number dropped between generations.
If you have a gaggle of friends all waiting to pile into a FIFA or Bomberman game, this is one 180 entirely in Microsoft's favor. Just make sure they bring their own controllers--unless you want to keep $480 worth of them lying around.
But whether either console can connect to eight or 800, what's really important is how sensually fulfilling each controller is to hold.