Also, I would like to point out that this was done before Garen's nerfs. The reduction in Garen's Perserverance passive (20% less regen) makes his strategy of 'hit and run' ludicrously impossible against Darius now.
But more importantly, the change of Courage to only scale based on Bonus Armor and Bonus Magic Resistance instead of Total Armor and Total Magic Resistance slammed Garen's ability to trade early. Garen has some of the WORST armor scaling in LoL; Garen has less Armor at level 18 than Miss Fortune, masteries / runes aside.
Garen lost about ~6 Armor at level 4, which equates to minus ~120g in stats.