I do get what you're saying but when a company buys another company they take both the good and the bad. They're taking on the liabilities of that other company. As far as I'm concerned, the Robin became Razers phone when they purchased Nextbit. Razer has been in complete control of whether or not the Robin gets security patches so I consider their track record with updates to be fair game. Also, the last update to the Robin dropped well after the buyout. Razer is aware that update left a crippling battery drain bug relating to Bluetooth that they have done nothing to fix. Again, to me, that goes on their support record.
Honoring a warranty is also part of an acquisition. And you're right, the ones on Amazon aren't being sold by Razer or Nextbit but the warranty cut off came before the last Nextbit sold units would have expired. All companies that I'm aware of still honor their warranties when purchased from other retailers if you have proof of purchase?
By the way, the Robin is still a great phone for the price, even without a warranty. I expect the Razer phone to be awesome. I'm just sceptical of Razer's support due to the way they've handled the Nextbit purchase.