The author's intent was to describe why they have to use a zygote process on Linux to watch over spawning new processes and why they don't need to jump through all the same hoops do that in Windows or OS X.
Another way to put it, more or less:
Due to Windows habit of locking files it has forced people to use a model of installing that avoids file clobbering issues present in Linux. Something else magically happens on OS X.
It seems to do the same thing in Linux with a system-wide package manager you would need a package manager that is aware of the processes that users are running, installs the software update to a alternate directory, sends a notification to users to shut down the application, and when they do that then rename the new directory over the old one.
Or something like that.
I am very interested in how iOS/OS X handles application updates through the app store. The blog posted hinted at versioning directories in the app bundle, but I have no clue what happens with iOS and such.