That's a pretty crappy excuse, I've had laptops that last for 7 years just fine running Linux.
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.
We're going through the same technology change with mobiles now, but that even seems to be tapering off now.