Why Macs are more popular now
The Ottawa figure is easy to understand: most computer technology people in Ottawa (not telecom people) get most / all / a lot of their business from the federal government, and being “compatible” with the feds is good for business. The federal government is a Windows shop.
Most people who use Windows are looking for compatibility not with the Canadian federal government, but with desktop applications they might want to install and run, most of which are available for Windows but often not Mac OS.
What do Web 2.0 people need to be compatible with? Mostly the Web, of course. Yes, some desktop apps are needed (like a browser!) but such necessities tend to be available for both Windows and Mac OS (not always from the same vendors). So Web-oriented people have the freedom to use either Windows or Mac OS, or GNU/Linux for that matter. And their #1 choice is the Macintosh.
(There are additional reasons for most people to prefer Windows: they need people who can help them out when they have computer problems, and most of those people are familiar with Windows and not Mac OS. Also, Windows machines are priced lower than equivalent Macs. Neither of these is an issue for the Web 2.0 elites.)
As more people become Web-based and not OS-based, there is the potential for a large shift in popularity from Windows to Mac OS. Particularly now that buying a new Windows machine means getting the excessively-featured (as usual for Microsoft) Windows Vista. I may make the switch myself when I get my next laptop.