I didn't say that Linux distros are NOT integrated, just that OSX software IS. Apple have control/influence over a lot of software that runs on OSX and all of the hardware, so this is possible.
Linux distros have many core apps that are nicely integrated, as you say, but whenever I am setting up a Linux box for my needs things inevitably come down to fiddling about with config files and scripts (ATi fglrx, anyone?). This, I guess, is a necessity from having an OS that can run on a whole spectrum of machines, rather than being tied to a handful of specific PCs.
Don't get me wrong, I appreciate what Linux offers me in terms of freedom and flexibility and undoubtedly, the integration and ease of use has increased dramatically in the past few years. My point is simply that OSX generally provides a better experience for a novice user, who wants things to "just work" (and work at their full capacity).
EDIT: can't believe I am arguing the pros of an Apple OS