Earlier quoted context omitted.
We have short lifetimes because TLS revocation doesn't work. It's that simple. To understand the distinction, imagine a password system where you can't change your password . You can make new ones, but the old ones still work. That's the problem TLS was facing.
Not quite that simple, no. It's a good reason, and while CRL and OCSP don't really work well - CRLite/OneCRL, CRLsets and valid all go some way to making revocation reasonably effective. Having an effective way to rotate all certificates, quickly, is a bigger reason. 1k -> 2k RSA took too long. SHA1 -> SHA2 took waaaaay too long. Changing anything about the webPKI takes too long unless everyone is on short lifetimes.…
Fair enough (I knew someone was going to come in here and whack me on this). I'd only say that this makes the overall argument for short-lifetime certs even stronger. :)