Since you asked...
Because I work at an advertising agency who is solely depending on QuarkXPress -- not be cause we want to necessarily, but because (like it or not) it is still the industry standard. In addition, try telling nearly a dozen "Creatives" that they have to switch programs and/or operating systems in order to be more creative. Most of us believe that creativity is a product of skills, not the tools.
Anyways... because most of the people who use Quark v4 do not feel like they need Quark v6 -- me included, to a certain degree -- we don't feel pressed to update to X. And because our IT department does not feel pressure, they don't stick their necks out with a $10K estimate for software and hardware upgrades.
So we work on near top-of-the-line G4 machines, running OS 9, QXP 4 and 5, Photoshop 6, Illustrator 8-10. And we make good money, do good work and win an occassional award.
Consequently, when I take work or other files home, I used to plug in my 2G iPod, mount it in OS 9, copy and transfer to my OS X (or 9) system at home.