My personal view is that with the introduction of SNAs, the chances of ordinary Platinums getting suite upgrades has diminished and the chances of a an ordinary Platinum getting an "above and beyond SPG Terms and Conditions" upgrade have shrunk markedly.

Platinums are no longer the most valuable guests: Platinums with Ambassadors or SNAs are.

The trouble with the OP's situation is that his expectations were a little unrealistic: he didn't grasp that "not available at check-in = no upgrade" and he didn't get that his only eligibility anyway was for a "Select Standard Suite", not any suite.

I think that we will see more and more of this with US airlines, as they fall in line with the rest of the world in making upgrades be something you spend tens or hundreds of thousands of miles to secure.