I just did that two days ago, the update situation being one of the reasons (the other that I like a reasonable quality dual SIM phone).
For now, it's just an extra phone to play with (Lumia 640, cheap, great build quality/performance for the price). But who knows ;).
I agree that new flagships would be nice though. Especially with Continuum.
Microsoft supports Windows versions for ten years, and I agree that's crazy for Android. However, three years I feel is a bare minimum expectation. Devices tend to remain on the market for about a year, and the standard phone contract is two years. So three years from a version release should cover the vast majority of users for the life of their device, should they choose not to take "system upgrades" which may slow their device or change it in an unwanted manner.
Vista, which actually came out in 2006 in the OEM edition Windows 7 Windows 8 Windows 8.1 Windows 10
Windows has had a much slower release cadence than Android. It's a much, much bigger burden on Google to continue to support older Android versions with bugfixes and security patches than it is Windows. Now, you can counter that Google decided on this release cadence, but still, I don't think it's reasonable to expect Google to support Android versions as long as Microsoft does Windows versions, as some here are stumping for.
(That said, every time I read an article about Android these days I get the urge to buy a Windows Phone.)