what's the deal with Google and app eligibility?

It took a good 5 days for my N4 to get the last play store update. I do not yet have the Hangouts update (its not yet 24 hrs since the release). I am in the US with an N4 bought in the US.

Forget Apple, even if we take Google in isolation. With all its server power why is it such a pain to distribute an app update to all targeted versions of your OS. So come to think of it, I am not sure its a server issue.

Then is it to ensure that in case something is wrong with the update, only a smaller batch of people are affected and the patch that can resolve it launched sooner? Not sure how they can control the target audience or manage the app/patch distribution.

Google is "usually" a No nonsense company. I just fail to understand this staggered app update model.

Or is it something sinister? I'll grab my popcorn while you guys weigh in.