At some point I imagine Verizon will simply stop supporting the phone, and the developer site will point to the last, 'carrier-blessed' OTA Android release.
If I can't trust a Nexus device on this platform, what can I trust?
I bought an AT&T Nexus S from Best Buy for $49 with a 2 year contract. It did not receive updates from Google even though it had a Google logo on the back and I had to update manually by downloading from the device image download link mentioned above. I have a Galaxy Nexus now that I bought thru Google, it updated to the latest point release as soon as I turned it on. As long as device gets purchased with a contract at a subsidized price, don't expect updates to get to you over the air.
At least in the USA that's often a sucker move. You pay full price for the phone, but still end up paying a higher monthly fee to cover the subsidized handset you didn't take.
A couple carriers do offer BYO handset pricing. But if you want to stick with a big carrier like Verizon then the phones Google sells directly are effectively coming at an extremely hefty premium.
Clearly, all hardware manufacturers have an incentive to not give updates in order to compel people to buy their latest devices. It's just that Apple plays a slightly different game by giving updates, which make your device slower and slower with every upgrade until about 18-24 months later, you just fork out cash to buy their latest device.