Where do you get that three years of support figure from? The only official numbers I've ever heard was 18 months, which lines up roughly with my experience.
I have a N5, which came out (just) less than three years ago, and it is not getting Nougat, which was released a few weeks ago. The last major update it got was around a year ago.
AFAICT with Google you're guaranteed to get the next OS version, if you're lucky you'll get the next next one (like N5 did with MM), but that's it.
Which, compared to iOS, feels pretty stingy.
