You'll have to forgive me for being an idiot, because I don't understand how that formula is applicable. If every point of crit increases damage by exactly the same amount, why would your return on damage slowly decrease as you approached 100% crit? Instead, wouldn't you maintain a constant rate of growth until 100%, at which point it sharply drops off (since a 101% crit rate is meaningless)?

In other words, critting 5% to 6% of the time should increase DPS by the same amount as going from 99% to 100% of the time. This is what the damage formula suggests. What am I missing?