Four years is a very long time for me to have one machine (my former turn around was 18-24 months) but if I had a machine from 2009 back I'd definitely be thinking about a new machine than wondering why Apple aren't supporting SL...there is a balance between being forced to update too quickly and those who take bloody ages to update holding others back!
Depends on the machine really, let alone the user. There were times around a decade ago where I would buy Apple hardware and find I needed to replace it just a few years later, if I was unlucky with where the technology roadmap was going. Eg the change from PowerPC to Intel chips.
The Mac Pro from 2008 I have is still going strong, and the Macbook Pro from 2009 only needed a SSD drive to make it feel like its still a very nice machine in 2014. Both of them have been upgradeable to the latest OS without issue. They have therefore proved to be more than acceptable value.
The first Macbook I got after the switch to Intel chips is still alive too and used by my mum, but it does fall victim to the inability to upgrade OS past a certain point and the looming lack of support for that OS. I am not going completely mad about this because of how old the machine is, and because its just one of those timing things, the first generation of their Intel-based tech that became obsolete rather quickly as things leapt on fairly quickly.
So some of the users who will suffer from Apples decision are in this group, victims of bad purchasing timing many years ago. The other small pool of people stuck on that version of OS X are those with a 'if it aint broke don't fix it' mentality who never went for upgrades, or those who are for whatever technical reason (including professional ones e.g. in the music industry) forced to keep a machine around with an old OS to ensure compatibility with their old hardware or old versions of apps.
I would still be happier if the likes of Apple and all other companies tried hard to squeeze out as many years of support for old hardware and software as possible. Of all the potential reasons why progress is 'held back', a company with the resources of Apple being forced to do patches for an old OS for several more years is very low down the list. I am a big fan of progress and new stuff in IT, but sneering at those who are moving through the world of IT at a much slower pace really winds me up. Those who do not wish to (or cannot afford to) hog the fast lane of technological progress are a completely valid section of the user base who deserve to be respected and whose needs should be taken into account by the products & tools on offer.
Despite personally embracing on many occasions the fetish of the new gadget, my wallet sometimes acts in accord with the above sentiments. I have for years refused to give Apple any money for a new iPhone because I thought they ruined the performance of my iPhone 3G at least a year too soon. And I will refuse to get another android phone for quite some time since they screwed my ability to keep my Nexus up-to-date after owning it for 2 years. I know there are often actual hardware limitations of certain generations of device that caused these unfortunate premature cut-offs, but even so as a strong believer that software has an important responsibility to keep hardware useable for as long as possible, I will put my money where my mouth is on this issue.