In fact, I would wager a bet that Microsoft made both of these claims based on the Insider program, knowing that even if the official update system remains unchanged, they kept their word.
I understand where you are coming from here. Really, I do. However, I'd like to provide some perspective.
Before a person can say "it's the carriers that stop the updates," let's look at how it all works. First, the reason carriers have been in charge of the updates for WP in the past is because of the hoops Microsoft has had to jump through and agreements Microsoft has had to sign to get their phones to be carried by the carriers. It hasn't been that way in the rest of the world, just mainly in the US. Yeah, another US only exclusive. I'll bet the rest of the world is glad to have missed that one.
If Carriers would be able to stop W10M updates, then they could also stop Insider program updates. The fact is, they can't, because the app itself takes it out of the carrier's hands. What Microsoft has done with W10M is to change it in such a way that the update path no longer goes through the carrier.
Most of the world doesn't have the "carrier interference" issues as has plagued the US. Unlocked phones are sold, and you can use them on whatever carrier you choose. Updates are from the Manufacturer, or, more accurately, the person who has provided the particular OS. Apple provides updates for iOS, Samsung for their "flavor" of Android, LG for their "flavor" of Android, "Google" for their Android in the more pure form. In the case of Microsoft, the OS is the same and not "flavored" like Android, so Microsoft would be in charge of updates, and they are bound by an agreement with US carriers to only update when the carrier agrees to it.
Why is Android so fragmented? Because the manufacturer's each have their own flavor of Android, and those manufacturers are the ones responsible for updating the OS. They choose not to. It's not carrier interference in the rest of the world, it is manufacturer apathy. They are responsible for updating the OS because they modified the OS, which means it can't be updated by Google.
With W10M, there will be ONE OS, not a bunch of flavors for each manufacturer. They won't be able to tinker with it and add their own flair like they do now with Android. Since it will remain a pure, unfettered OS, Microsoft will be able to effect the upgrades.
But what about the carrier agreements in the US? Have you noticed what has happened? Microsoft has broken off with all US carriers except AT&T. AT&T has been the most cooperative. I think AT&T has agreed to Microsoft's terms here which is why they are being allowed to carry the Lumia 950. All carriers in the US have been informed by Microsoft that their agreement to upgrade any handsets under that carrier's control amends the agreement that once the phone is on W10M that the carrier relinquishes control of updates. That may make it difficult to get some US carriers to agree to upgrading to W10M, because those carriers want to sell you new phones, not extend the life of your old one.
My 2 cents according to my understanding of the industry. My understanding may or may not be exact, but I "believe" it makes sense, hence I "believe" it.