Because it's the average maturity (in years of age) level of 75% of the community
It's not only about balance. Certain attack animations become really messed up past 2.5 AS.
Usurp the Throne
Ever see a Nautilus with 2.5 (or hell, anything beyond 1.5) attack speed?
Swings that massive 10 ton anchor like it's a twig.
anyone remember the maximum AS Sion/rageblade bug? yeah... that would have been crazy with no cap. INFINITE ATTACK SPEED
Fox P McCloud
In DotA the max Attack Speed is 2.63 to 5.0, depending the hero...that said, the vast vast majority are capped at 2.94 AS...only one hero can hit 5.0 AS (Alchemist).
In DotA, additional AS is capped, not the total AS (ie: as an example, you could stack as many phantom dancers as you want, but you could only have 300% AS).
Random fact: LoL took the armor and attack-speed formula's from DotA----they just flipped things around to make it seem different, on the surface.
© 2013 Riot Games, Inc. All rights reserved. Riot Games, League of Legends and PvP.net are trademarks, services marks, or registered trademarks of Riot Games, Inc.