It gets said a lot that there's rarely anything really new in football. Every strategy or tactic has been done before in some form or fashion, and we're all just finding new ways, or twists on old concepts. Air-Raid passing teams use pass plays popularized by LaVelle Edwards at BYU in the 70s and 80s. Most spread running games uses concepts and theories that worked for the single wing, wing-T and of course, various option offenses.
So when myself and other pundits talk about the whole "spread vs. pro-style" distinction as largely arbitrary, at least in terms of how they're commonly used, it always comes back to this central tenant that has defined offensive strategy in this game ever since the flying wedge was outlawed in early days of the 20th century: an attempt to give a team a numbers advantage in an 11-on-11 game.