I can't fathom why the place where the device was purchased would matter if it's a Google phone. Apple manages to support iPhones whether you purchase them from an Apple store or in a back alley for bitcoins.
I know this is semantics, but it's fair. Apple doesn't manufacture anything, they design products and contract out the manufacturing to Foxconn. Basically the same as Google contracting out manufacturing to Huwei, only I think with the Nexus products it was more of a design collaboration than with the Pixel line.
Apple is the manufacturer that is honoring the manufacturer's warranty (and/or additional warranty options). Google is not the manufacturer of the Nexus 5X/6P, that's Huawei. So if you didn't buy from them, they send you to the manufacturer, like most retailers would after the initial return window, even if you did buy it from them.
I agree that it's bad for Google's image to operate that way, stick their name on a phone and then shrug their shoulders and tell you to talk to the real manufacturer. But that distinction is why Apple supports most iPhones no questions asked, and Google wants to know that you bought it from them. They're a glorified retailer licensing out their brand to Huawei.
I get it, but it's essentially Google wanting to have their cake (marketing to customers: "It's a Google phone! Pure Google all the way, baby!") and eat it, too (product support: "Uhhh, yeah, we uh, we don't make this thing, it's all Huawei, we're just a humble retailer."). I agree that it's absolutely bad for Google's image to operate this way, as you can see from the comments in this thread. People aren't mad at the OEMs Google paid to manufacture their devices, they're mad at Google.
> the OEMs Google paid to manufacture their devices
I'm not 100% sure, but I don't think that's how it was. LG's Nexus devices were manufactured by LG for LG, etc. The "Google" part of a Nexus phone is the software and some collaboration in the design.