Now, I know that most Mac users don't really care whether they can rebuild the kernel or not -- truth be told, I've never bothered to rebuild the kernel on my G5 iMac, and I've never really had the desire to. I could argue that the ability to do so is important, but most users don't deal in abstractions. So long as they don't see a practical use, it doesn't matter.
The practical argument, for users, against the closed kernel is Apple's insistence that if I want to run Mac OS X, I've got to buy the hardware from them. Even Microsoft, no slouch when it comes to corporate arrogance, is pretty casual about the hardware Windows XP runs on.
So long as you've paid up your license fee, Bill and the bean counters in Redmond really don't seem to care if users run Windows on hardware from Dell, Gateway, Hewlett-Packard, or Bob's Computer & Bait Shop. That's not good enough for Apple, though -- if you don't buy the entire kit and kaboodle from Apple, it doesn't want your business. For Steve Jobs, it's all or nothing. That might explain how Apple lost its lead in the personal computer business in the first place.
Maybe Microsoft should follow suit and restrict sales of Windows XP, and Vista if it's ever released, to hardware specifically authorized to run Windows from Microsoft-approved vendors, but most definitely not Apple hardware. Something tells me Apple, and its legion of fans, would feel quite differently about being told "no Windows for you!" on Apple hardware.
Won't you please think of the Apple hardware sales?
What really amuses me is the attitude from Mac users that Apple deserves to "protect" its hardware sales from users who might want to use its OS on hardware they choose. Apple isn't giving away its OS, even to users who spend the bucks on Apple hardware. For example, users who purchased new Macs before Mac OS X 10.4 ("Tiger") was released get the privilege of plunking down $129 for a copy of Mac OS X 10.4, or $199 for a "family pack" for five licenses for homes with more than one Mac.
Is Apple really going to go broke if thousands, maybe millions, of users run out and buy a copy of OS X to run on some other Intel-based machine? Of course not, but they might not get the profit margins off of selling the hardware and OS X upgrades as the users try to wring every last dollar out of the hardware.
Linux-haters like to equate the GNU General Public License with socialism and communism, but it seems to me that Apple's the company with the anti-free market business model.
Bring your own hardware
Ultimately, this is one of the reasons I could never be full-time Mac user. It's not that OS X is a bad operating system; in fact, OS X includes most of the components I'd want out of a good Linux distro. But I don't have the freedom to use the system the way I see fit, the way I can with Ubuntu, Fedora Core, SUSE, or Debian.
I like being able to put together my own machines and have a few options when it comes to the operating system that I use. Apple's hardware options are far too limiting for my tastes. I can easily put together a system that runs Linux like a champ for less than $1,000, and with the options that I choose, not the limited set of options presented by Apple.
What's more, I can upgrade the system regularly with new components without needing to run out and buy a whole new machine when things get a little sluggish. I can plop in a better video card, or slap in an additional hard drive or DVD recorder, or maybe find room for an expansion card -- something that's tough to do with Apple's slick but cramped iMacs and Mac minis.
The FOSS community, however, is all about options. Want to run Linux on a Mac? OK, we'll support that. Want to run Linux (or BSD) on UltraSPARC, Itanium, PowerPC, AMD64, and x86 hardware, no matter who the vendor is? We'll let you do that too.
Apple may be using open source, but it's not an open source company. Despite the occasional contribution to open source projects, Apple's behavior is ultimately no better than Microsoft's. Closed is closed, and users should vote with their dollars for an operating system that gives them options, not restrictions.