Apple developer intermediate certificates are expiring Feb 14, 2016
developer.apple.com
developer.apple.com
Note that Mac OS 10.6.8 is the most recent OS version for the Intel Core Duo Macs. Those are the first MacBook (early 2006), the first 2 MacBook Pros (January 2006, May 2006), two Mac Minis (February 2006, September 2006), and two iMacs (January 2006, July 2006).
It also affects people who keep Snow Leopard 10.6.8 for sentimental reasons. Apparently 1 in 5 Macs use Snow Leopard. Not being able to receive new app updates could be troublesome.
http://www.computerworld.com/article/2487996/malware-vulnera...
According to an article that's almost two years old. I doubt that number is so high today.
I do have a PPC Mac too, but with Nvidia graphics, so Linux is not a solution for me :(.
It's the same theory with passports, credit cards etc.
Without expiry dates on certificates, we're stuck with trusting whatever we've issued forever. Lists of revoked certificates would grow forever, and work even worse than they do today. At least now, we can stop worrying about ancient certificates after they're expired.
Having certs expire and be reissued also ensures there's a continual path to upgrade to newer certificates: I suspect you'd have a much harder time retiring SHA-1 certificates if nobody had any regular-interval incentive to replace their certs.