I'm pretty sure I remember seeing this change requested by somebody.
Hate to link to reddit, but here's an example of somebody complaining about the new q animation on butcher urgot specifically: http://www.reddit.com/r/leagueoflegends/comments/2evqck/urgots_butcher_urgot_skin_no_longer_has/
Prior to 4.15, there was the added bonus that Urgot's Acid Hunter would now fire chainsaws, spinning on an axis perpendicular to the blade of the chainsaw and parallel to the ground, defying all common notions in combat where the blade of a weapon should consistently hit the opponents. This fiercely intimidating animation struck fear into the hearts of your enemies.
Now, in a pitiful display of weakness, Urgot fires the chainsaw on an axis parallel to both the blade and the ground. How could this injustice be called upon? Has Riot Games gone mad?
Don't have an opinion on this personally (battlecast urgot user), but the point is Riot may have thought they were catering to the preferences of butcher urgot users by reverting the q animation.