When I first wrote the article, I wasn't aware that things like /System/Library/LaunchAgents/org.openbsd.ssh-agent.plist existed prior to Mavericks. Shouldn't detract from the value of the article though which is to add Notifications. Last Mac I had I didn't recall it automatically launching a Keychain aware ssh-agent on-demand.
What's changed is that in Mavericks (really Mountain Lion or higher) we have the Notification Center. No longer do we have to rely on 3rd party software such as Growl to get notifications. However, Apple has not yet hooked ssh-agent into the Notification Center. This blog starts off kind of slow by first introducing folks not familiar with the existing Keychain/launchd integration and then goes on to follow that up by talking about future integration with Notification Center (providing working code and binary for others to experience a Notification Center aware ssh-agent).
--
Devin
As for the OpenSSH version, Apple forks OpenSSH and then adds things like Keychain and launchd(8) support. So if you want a later version while retaining those features, you'll have to get Apple's customizations applied to a later non-Apple version or wait until Apple does it themselves. Migrating my changes into a non-Apple version simply to say you have the latest version of OpenSSH would mean that you lose keychain and launchd(8) integration.
--
Devin