I've been using a Mac since I got my first Mac Plus, and I've been using Mac OS X since OS X 10.1 came out (since that was the only usable version on my computer). I love OS X, but I can understand why people don't want to move to OS X.
What it all boils down to is change. Mac OS X is the epitome of the word "change". UNIX underpinnings, totally revamped interface, new ways of doing things, totally different menus in the Finder, Dock, new Apple menu, etc. People are ingrained into their Mac OS 9 habits and they don't want to take the trouble to learn the Mac all over again (even though it isn't nearly that hard to learn Mac OS X from Mac OS Classic as it is to learn Windows from Mac OS Classic). But when you immerse yourself in OS X and learn how to do things, you'll find yourself loving it, and doing things much faster with OS X.
Come in. The water's warm. Or should I say, the Aqua's warm. :)