Of course they need large scale manageability. What the GP post said was that there are no tools that offer the facilities that AD and GP do on Windows. You can do a whole lot of stuff with scripts and other tools, but that doesn't mean it's as straightforward.
The real strength of GP is the ability to modify the way the software that runs on top of Windows works, not just the OS itself. Of course, MS offers the best support for that in things like Office, although other applications can be managed too. With the sheer variety of mechanisms for configuring applications on Linux, there can simply be no equivalent.
Offer me a working equivalent of GP, and an Exchange replacement, and I'll give it serious consideration. Until then, for me, it's just not worth the hassle.