Attack Speed per Level

AS/lvl = + (coefficient * AS_growth) . . . . where . . . . coefficient = (1 / 400) * (7 (level^2 - 1) + 267 (level - 1)) -- http://leagueoflegends.wikia.com/wiki/Attack_Speed

Riot, why is this formula needlessly complex? It's barely superlinear. I.e. a plot of Coeffient vs Level is nearly identical to (y = x - 1.8). While I can imagine the reasoning behind Attack Delay, I can't imagine why the AS/lvl Formula scales polynomially.

Motivation: I've been comparing AS runes and AD runes using spreadsheets. Initially, I assumed AS/lvl scaled linearly just like with runes, masteries, and items. E.g. Trinity Force gives 40% AS. If I buy it, my total AS is increased by + (40% * base AS). To compare runes, I wanted to calculate marginal damage to gold cost. Looking up Gold Efficiency wouldn't be enough by itself since AS and AD interact with each other. Additionally, AD and AS vary directly with levels. To get the clearest picture, I'd need to factor in AD/lvl and AS/lvl. But I couldn't figure out where the numbers on LoLwiki's List of Champions' AS were coming from.

While inconvenient, the formula isn't a huge problem to my theory crafting. At this point I'm asking more out of curiosity.