My personal opinion is that, unfortunately, regulation is the only way to solve that issue, as the market does not appear to be addressing it well.
But wait I'm novice who can't decide what is best for himself :(
Apple patches the newests version of iOS. Sometimes older versions get a security update here or there, maybe. So you'd have to be running the latest version of you want security fixes. Which isn't always possible due to compatibility or performance/stability.
If your iPhone is 3 or more years old you can forget any support from Apple whatsoever.
Why not please your customers? Give them what they want? I don't even think the average customer would need a TOS of all the negatives using an older operating system brings.
They have a huge war chest. If a customer wants to be on the operating system that came on their device ten years ago; why make it difficult?
Could it be they want us to upgrade/buy regularly? For myself, I don't think I will ever buy another new Apple product. I will still give them as gifts though.