I don’t know if that’s true - I use a Nexus and it’s well supported in terms of updates - but I actually think it might be the way to go anyway. I would quite like a situation whereby my phone gets minor and patch releases, but I have to upgrade my phone to get the next major. That way, I can have some confidence I’ll get vital security fixes and minor features without huge performance penalties, and each major release can be very highly optimised for the latest hardware.
It is absolutely true. Outside of a few model lines which get directly supported by Google, software updates for Android phones are rare. This is one of the biggest causes of Android fragmentation -- for most people who have an Android phone, the version that came preinstalled is the only version that phone will ever have installed.
It is probably that Android users usually do not receive updates, so they can't complain that updates made their phones slower.