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.
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.
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.