Ermmm... it is FAIR!
At the end of the day, they don't make a Cent from OS upgrades, but they cost millions to develop and support! The biggest problem with Macs, from Apple's point of view, is that they are just too good: They are very reliable - even the battery life on my 6 year-old MacBook Pro is still probably 75% of how it was when I first got it - and they are timeless in their design. They are so well built that they don't fall apart (like 3 successive Sony Vaio's did before I switched) and Hard Disks don't fail. They don't get virusses that wipe your hard disk, so you feel compelled to start again, afresh and they are fully upgradeable for years, without loss of function.
People like us, who were the 'Early Adopters' and evangelists that got everyone else to switch, are now the thorn in Apple's side, as we never buy anything new! So we now COST them money, rather than make it any more (especially when we put potential new customers off, with our complaints on these forums!)
Having said all that - forcing people to upgrade by rendering their old machines unusable - is the most unpleasant form of marketing in existence... Much better to TEMPT people to buy new machines, with exciting new features, not available on older ones... Thunderbolt could have been the temptation for me, but it's pants as no-one makes any peripherals that exploit its advantages and, within weeks of its announcement, USB 3:0 was launched and almost as fast! If I could have obtained a Thunderbolt memory card reader 4 years ago, I would have updated my MBP there and then!
So, come on Apple - give us some hardware that will tempt us to change, rather than annoy us all by killing our trusty old machines... At this moment in time, for me, my MBP gives no advantage over a modern PC (in fact it is seriously compromised, with all sorts of bugs popping up with 3rd party software, as the OS gets ever more complex and Apple-centric - e.g. the Adobe Creative Cloud issue that surfaced recently!) So, if my MBP dies today, I suspect I will spend half as much on a PC that will perform much better than what I am used to 😉