I think historically Apple has supported hardware better than software. In some cases just the latest OS is fully supported with security updates. Our Macbook Pro Early 2008 has survived longer than any other Apple computer we've owned (and we've owned since late 80s). I've upgraded it with SSD, maxed out RAM at 6GB (4GB could barely run Yosemite). Quite expensive computer (and even more so here in Sweden), but worth the money. At the moment it runs great, but I guess lack of security updates for El Capitan and its Safari will force my MBP into retirement in 2017, 2018 latest. Addition: I wouldn't mind staying on El Capitan for years to come if Apple promises security updates until a certain date, just like Microsoft does. I do _not_ like Apple's quiet drop of support for older OS.
I would accept this without question if Apple offered a good explanation. Lack of drivers for <whatever device> or something would do. Too little RAM for the GPU (I have 256MB). What should kill many old Macs is lack of RAM I reckon, being stuck with 4 or even 2 GB today isn't fun. If they say they drop it because they can't be bothered to update Firewire,bluetooth or camera drivers I'd be annoyed though, as those are features I never use. And I'd like the choice to upgrade and lose some obsolete hardware support, just like Windows allows. (I have hopes that there will be ways to force an upgrade to "obsolete" machines)
As for other platforms. My 2012 Google Nexus 4 phone, with quad core CPU, 2GB RAM, HD display, whatever, was dropped by Google "for no apparent reason" when Android 6 was released 2015. Although hardware of my Nexus is still better than many 2016 Android phones it is stuck on a 2014 OS (Lollipop 5). Apple supports phones better, removing features but giving ("forcing") older phones new operating systems and security updates. (I now use Custom ROM for my phones, but Samsung, Google, LG, Sony, they all have crap update/upgrade policies)
Ok this is OT, but I run Windows 10 on a 2010 8GB RAM quad core intel PC with SSD, it also runs OSX El Capitan. No problems. I expect it to run Sierra, but perhaps the GPU (AMD6670) might kill it. I will then upgrade GPU. I also have a slower 2009 quad core AMD PC with 4 GB RAM and a cheap AMD 4650 running Windows 10, SSD, no problem, kids use it for games and TV. And I have a 2006 dual core AMD with 4 GB RAM and nvidia 8400 running Windows 7 (which MS supports with security updates until 2020). It might run Windows 10 if I tried, but I haven't. My point is that PC hardware also survives long these days, unless you buy the absolutely cheapest stuff available. I think my 2010 PC run Windows 10 and El Capitan better than some current line PCs and Macs actually. None of my PCs have anything but "standard" equipment", they were all quite cheap and then upgraded as needed. By far our Macbook Pro is our most expensive computer, and it runs El Capitan without problems so I'd like Apple to give us the choice to run Sierra if possible.