To put it another way: if you learn of a very serious exploit like this in the wild and an upgrade is the only way to solve it -- by all means, go ahead and upgrade. I'm not saying you should never upgrade, nor am I saying serious security vulnerabilities cannot pop up. But neither in any way implies you need a periodic 1-2-year hardware/OS refresh. A refresh could be justified in 1 day or in 10 years; it just depends on what the actual threats and mitigations are. Remember what the original discussion was about: it was about whether the periodic refresh is justified.
As for the rest of those (StageFright and other attacks) -- I've addressed them in other comments. See here: https://news.ycombinator.com/item?id=15040745