Huge in what way? Obviously for you, you prefer Mac OS X. And you know what? That's great. It really is. You should always use the OS that works best for you. But for millions of other people, it's Windows Vista that works better for them. And again, that's great.You're apparently incapable of missing the point, too. The hardware is very similar (not quite the same because of EFI vs BIOS, but similar). But the OS is very different. The OS is what determines usability - and the difference between Mac OS X and Vista is huge.
Yes, the hardware is very similar, and yes, the OS absolutely makes the difference. But you know what else makes a huge difference? The end user. Here's a quick example. I have an iMac in my house. When I use it, I can get my work done quickly and easily. But when my sister uses it, she isn't as quick on it. And she's told me that she prefers Windows because she likes the way it works better.
The point is that at the end of the day, there really isn't one end-all, be-all, OS. The OS that works best for you is the OS you should be using, and that's what makes people perceive one OS as "better" than another.
And I guess that's the point I've been trying to make all along. Some will see Vista as a dud, others will not. I don't.