It's a bit different though isn't? Updating versions on your phone is more like upgrading to the newest service pack instead of buying a new OS. The OS is available for anyone to grab free of charge, updated patched and new features even. Free of charge.
That's not the same as letting support of XP die and quite frankly I had no problem with it in the first place. That OS is decades old now and the people bitching about security holes were most likely using it for custom software that was probably just as buggy as the OS at that point. I know first hand it can be hard to get custom software companies to update their software but it's not Microsofts fault either.
If the people who take Android and put it on phones are unwilling to release updates for it, that's the vendors fault. They take Android and fork it to suite them, then don't bother updating it when a new version comes out. That's how open source software works when you think about it. The main distro is out there free for the taking. Vendors take it and fork it how they see fit, it no longer is the main channels responsibility.
If we have a problem with this, we are really talking about having a problem with opensource software. Then we can discuss the other issue which is when do we can support on outdated versions?