Because people that truly know and appreciate technology are not brand loyal and will have a mix of most everything on the market if it works right and is designed well.
Some guys at CNET were talking about wanting to own both platforms. Makes sense, although I'd prefer one seamless integration but until I can break these MS Office bonds (which I don't see happening any time soon)...
It's really not bad. I have full calendar, document, phone, email and tasking platform integration going great between my Windows desktop, Droid Incredible, wife's iPhone 4, iPod Touch, iPad, and MacBook Pro, on both the Mac and Windows sides. I can enter any item on one of those devices and it will transfer all platforms perfectly. In the calendar, task, email and phone situations, it does it instantly with push integration. There are some great conduits out there now.