The Linux-bashing is quite funny (I've seen worse on other Mac-sites on that topic, but still), it shows that even UNIX users have no idea what Linux is. I would have expected uninformed crap from a Windows forum, but it seems Mac fanboys are worse...
1.) Linux' scalability is way better than Darwins. A regular, of the shelf kernel runs on everything from a PDA to a 256 CPU Itanium2/ Myrinet supercomputer. It's also more powerful and faster, and tweaked for low-end and embedded systems. Running the GNU OS on top of Darwin instead of Linux would be very stupid, as Linux is leaps and bounds beyond. The only reason Apple choose Darwin/ FreeBSD was the license, not technical merits.
2.) The MIT notebook won't use a regular RedHat Linux, RedHat engineers are designing a custom distro for that specific notebook.
3.) Linux is not hard to use or set up. It could be as easy as OSX, or even easier. It depends on the platform and the designated use. Since the distro will designed for that notebook, installing it will be as easy as it gets, as there's no need to configure _anything_.
4.) The MIT choose Linux for several reasons (flexibility, availabilty, cost), but there's more. The open source idea is a major factor. The community will testdrive the software, will make additions, suggestions, will fix bugs - for free. Even if Apple were willing to offer equal support, they could never afford it. There's lots of software available for free, in many languages. Is OSX available Khmer or Vietnamese?
5.) Of course, the spirit of open source is also an issue. If the people that work with those notebooks understand that software and information should be free, and since the MIT intends to even ship basic programming languages and IDEs with their notebook, there's hope that people in Cambodia or wherever will join the community.
So, Linux is the only viable option. Bill knows that, Steve knows that, everybody knows that. The offer was a marketing stunt. A bad one, I might add, because Apple knew the MIT would turn it down. The MIT asked for screwdrivers, Apple offered free pencils. That seems nice, but it's not what the MIT needs. So, the offer either was a stunt or stupid...