I've never seen any figures compiled, but I know that the efforts to get people to climb up into the balconies and loges of older days got to the point of the ridiculous to make such seating work. Look at the case of the long-lost MARBRO in Chicago: a double sided, double flight, split level flying staircase that brought its marble glory up three stories! This may be a far cry from cinema stadium seating, but it shows what the early designers knew was necessary to entice people away from the main floor so that they could sell some of those seats that had great views.
Look at any older person closely from a distance, and you will notice their legs wobble slightly as they move, but especially as they try to climb steps. For those of the elderly who are more spry, the steps may be no big deal, but for most elderly and the very young (not to touch the hot topic of wheel chairs) steps are something to be avoided! Yes, I like stadium seating's sight lines too, but then my legs work, so far, (though my heart and lungs are failing), so steps may work for this old bird for a while, but for how many others? If your only aim is teenagers, then don't fret; they will gladly climb anything!
[This message has been edited by jimor (edited October 03, 2005).]