@Michael Fremlins and other comments
How many people in a corporate environment actually use Photoshop, Illustrator or Quark. Also, the fact that you mention Canvas 7 as an app you use shows that you are not a normal corporate user.
Most people in places I have worked use the following apps.
Word processor, Spreadsheet, Email, Calendar, Web, Internet/Intranet access and Some way to access file on the network
All of this can be done by any desktop OS today. It's just the inertia of Windows and Office and the fact that people don't like change.
If given the choice of keeping things as they are or changing people will keep things as they are. Case in point is the comment from @Hugh_Pym about the typist.
Changing will get resistance.
I expect from a support and management standpoint there are a lot of Windows Admins out there, but far fewer Linux admins, not to mention desktop support staff. People go to your comfort zone. Back to inertia. Windows admins and desktop support teams will recommend sticking with Windows because that’s where they are most comfortable.
The shift in what we use is happening slowly. Firefox is growing, OpenOffice is starting to get its fans, Googledocs and Gmail are popular. The need for it to be a Microsoft centric environment is decreasing and so the potential to use something different is becoming more appropriate.
Finally, I heard a great comment.
How many of us are using the same operating system and applications as we did when we joined the great unwashed workplace.
I used Windows 3.1 with Office 3.0 Looks a bit different to Windows XP with Office 2003. From an admin standpoint it is completely different as well.
So, in my opinion people can change and get use to new apps and ways of working, the problem is the move from Windows to Linux on the desktop is sold as a big thing when for most people I think it really isn’t.