Hearthpwn

I think I read somewhere that they didn't give Witch's Brew Echo because, when Witchwood will rotate out of standard it would become the only card with such a mechanic, SN1P-SN4P is considered as a Boomsday card and as such it will rotate along the Echo mechanic. However I still can't grasp why Y'Shaarj, Rage Unbound  doesn't have Recruit (Old Gods was released in the same year as Kobolds) and especially why Charge doesn't give Rush (naming aside) since it's a continued mechanic.