Sooner or later you will have to buy a new device due to planned obsolescence, i.e. when (security) updates are no longer released. But then you can of course install a free operating system instead.
I was purposefully leaving Macs out. My 2006 era Core Duo Mac Mini stopped being supported in 2008 (?). I was able to install Windows 7 on it, give it to my mom and it will still be supported until 2020 by Microsoft...
You do bring up a very valid point but I think that is true with anything that consumers buy like cars, or common household products when things just start to break or newer iterations of those products come out with better features.
But why throw something away which is not physically broken? I currently use a Mac Mini from 2009 with Debian and I have no complaints... well, except that software keeps getting slower.
