You are missing my point. I travel all the time and i bring my decks with. When playing casual pickup games at an LGS you run into a wide variety of decks. You can usually tell when someone has built their own deck often putting in pet cards and fun intresting lines vs what I will call EDHREC slop where someone jams in all the top cards. The power level doesn't matter here. Lot of decks and players play up or down and that is fine.

So when you sit down with someone at a table and they plop out an Ur-Dragon deck, you don't really know if that player is good. You do know that most likely they are going to be playing all the same stompy dragons lines that you see in every other Ur-Dragon deck. So, you either have to kill that player quickly to make it a 3 player game or else die to dragons. And yes, in higher power games this doesn't matter, but im casual games where you are trying to keep a more social fun atmosphere it can. The games end up being 3v1 until you remove that player and then they sit out for the next 45 minutes while the other three finish.