That was not true for Windows 10 Mobile. Some devices never received the update.

What was indeed the insult on top of the injury - the WM devices were all Qualcomm Snapdragon devices. They were never so varied as Android devices are.

It was not true for Windows Phone 8, and therefore some carriers interfered with the deployment of the upgrade. It is true for Windows 10 Mobile, however. If a device is supported for Windows 10 Mobile, all updates are carrier independent. The "Upgrade Advisor" app Microsoft released to the Windows Store effectively allowed you to circumvent the carrier and upgrade to Windows 10 Mobile, replacing the Windows Update source for your phone with Microsoft's.

Ah, so that is how it went. I knew some devices WP devices (didn't note version) never received the updates.

However, the part about them all being the same Snapdragon devices with slightly different cases, cameras, etc. is still true. Microsoft doesn't have to solve how to make a release for Exynos, Kirin or Tegra devices.

The other neat thing they did which included WP8 was that their Developer Preview would do the same thing with the Windows Insider app. If you signed up for test builds, you'd get updates regardless of model or carrier, to the latest build offered. (And a lot of never officially supported phones can use Windows 10 via this method.)

That being said, this was only kindasorta a good thing, because it didn't always have working third party drivers attached. My old Samsung ATIV SE was super glitchy, particularly in the touchscreen department, when I upgraded my phone absent Samsung's blessing.

But it was one more place Microsoft kinda demonstrated even their mobile OS builds were more or less hardware independent, which is a huge contrast from Android.