Before now, it seems that the game designers never sat down and calculated things like a characters chance to hit normal foes as they progress from level 1 to level 20. Things like full, 3/4, and half BAB progression were implemented because they seemed to work, and because they worked well when laid out on a table, not because of number-crunching that determined they were the best way to balance classes. Similarly, Acs were given out that seemed appropriate, but, were not calculated into an overal scheme of gameplay. The mathematical playability of the game was never thoroughly appraised by the designers until 4E.