I'd regard Nexus and Pixel phones to be the equivalent of iPhones for something like this - they get updates directly from the "manufacturer"/Google, much as iPhones get updates from Apple.

Samsung-branded devices sold primarily through carriers on the other hand get updates when they finish passing through the system of Google->handset maker->carrier and often both the handset makers and carriers are big delay points.

(Almost?) no one has that update yet. Sample size 1.

That's strange, do you have auto-updates disabled? My understanding is that it was immediately released. My Nexus 6P has it, I got it the same day it was released or a day after. Screenshot of my About Phone screen:

http://m.imgur.com/APSvk8Z