Is there anything that Debian does with regards to integration that Ubuntu, Fedora, CentOS/RHEL, and even Gentoo don't do?
Another example: The Debian packaging guidelines demand that every executable have a man page available, even if the upstream project doesn't supply one. They're not always as complete and comprehensive as one might hope, but they're often enough to give you the general gist of what a command is supposed to do, and how to use it.
Yet another example: Debian has an 'alternatives' system, by which you can configure the system and tell it that your preferred terminal emulator is 'xterm', your preferred text-editor is pico, etc. (this extends to man pages too - if you make "x-terminal-emulator" point at xterm, then "man x-terminal-emulator" will give you the xterm man page). Every package that Debian ships that is able to spawn a terminal emulator in some way is required to launch x-terminal-emulator rather than hard-coding xterm or rxvt or whatever.
The downside to all this is that if you know how to configure/administer package X on RedHat or FreeBSD, you might get lost trying to find where the package keeps its stuff in Debian. The upside is that if you know how to configure/administer package X on Debian, you should find it pretty easy to configure/administer packages Y and Z as well.
One more example: The last time I installed fetchmail on RedHat, I wound up having to create /root/.fetchmailrc and write my own cronjob to run it. The last time I installed fetchmail on Debian, it already came with an /etc/init.d script that would do all the periodic checking for me, all I had to do was create an "/etc/fetchmailrc" file (like any other system service) and start it up (like any other system service). Debian's integration goes far, far beyond any other distro I've seen.
To a large extent this is also the Debian model, which is a lot more integrated than many Linux distributions--- they don't just cobble together a bunch of packages and call it a day. Like FreeBSD, they do take a lot of things from upstream (e.g. both use X.Org as their X11 server), but also like FreeBSD, they heavily customize the core packages and develop them so they work together well. There are core Debian teams working on its versions of the Linux kernel (http://wiki.debian.org/DebianKernel), X.org (http://wiki.debian.org/XStrikeForce), Exim MTA (http://wiki.debian.org/PkgExim4), package manager (http://wiki.debian.org/Apt), etc., along with thousands of Debian-specific patches to other packages, which are maintained as far as possible in an integrated manner to meet the unified Debian system policies.
It's not entirely identical, but I don't think it's that far off. I think the FreeBSD core system may be developed somewhat more as a single entity (for example, because FreeBSD literally develops its own kernel, rather than customizing an upstream one), but Debian may actually have more cohesive development across the entire system. My impression, though I could be wrong, is that FreeBSD ports are more spotty when it comes to really being managed seamlessly with the base system.