Nope, not quite!
I use Leopard and XP on my iMac at home, Leopard for almost everything, but XP for Ruckus (a music service for college students) and for gaming.
On my Macbook, I use Leopard primarily, and Fedora Core 9 just to play around with Linux.
Then I use XP on my work laptop, but we're thinking of switching over to Linux thereabouts as well.
While I'm as big an Apple fan as any, I still firmly believe that each OS serves its own purpose, and that there should NEVER be a monopoly on operating systems. People will always want variety, and no OS is perfect for anyone.