Let's get closer to comparing apples to apples. Every one of my laptops has lost manufacturer support 1-3 years after I got them...but even my 13 year old laptop will run a current Linux build.

Every one of my phones has lost manufacturer support 1-3 years after I got them...but my 5 year old Galaxy Nexus still has Cyanogenmod builds being released for it (based on Marshmallow).

With the timelines of when these different markets began, I think that's a fair comparison. Manufacturers want to maintain as few models as possible, but the community often does the work to provide extended support time.

Laptops aren't mobile phones though. Phones have seen much, much more change in the past seven years than laptops have.

Not in the past couple years though, there is really nothing significantly different in the hardware of a Samsung Galaxy s3 and a Nexus 6. Also, one of those laptops was manufactured in the late 90s.

Well, not anymore. Laptops, and computers had huge change from the 70's to the early 2000's.

We're going through the same technology change with mobiles now, but that even seems to be tapering off now.