You'd think so, but it's not like that. I play pick-up roller hockey with a bunch of guys at a rink near where I used to live. It's really informal, so we don't get too tired out there. I'm a much better roller hockey player, because I in-line skate a lot more than I ice skate -- so it doesn't tire me out very much on Saturdays.
Ice skating is much harder on the legs, so I tire out easier when I do that.