In all due respect Narrator is not a screen reader and Microsoft never claimed it was. To gain access to the OS in Windows you will need to buy a Windows screen reader which will add a thousand dollars to the cost of what ever computer you will buy. Or put another way you can buy a entry level Mac for less than the cost of a Windows screen reader itself.

While many here have said that VoiceOver is not as capable as it commercial Windows counterpart I would beg to differ. VoiceOver is fundimentaly different from Windows screen readers in several ways:

VoiceOver is a integrated part of the OS. Therefor it does not attempt to step in an do tasks that the OS does. So it does not need commands to close a window, for example, as the OS provides that already.

Second in Macintosh it is the applications that are changed to become accessible with the screen reader and not the other way around. So we gain accessibility each time a developer follows the rules and improves his applications (Microsoft did you hear that? Microsoft Office for Mac is not accessible but OpenOffice 3 is.)

I would also point out that VoiceOver support most USB braille displays without having to install drivers for them. Anyone who has ever tried to get a braille display running under Windows will see the improvement in that.

Now I'm not one of these Mac fanboys who will urge a Mac where it is not appropriate but for many blind users, and for most dyslexics who require a screen reader, who have usual computer need and who do not need a Windows computer for some specific task a Mac should be considered. It will perform the basic tasks, will cost less at the outset and will cost far less to upgrade over time as there will be not screen reader updates to buy. They support braille. They are less prone to spyware and such and the out of the box voice quality is hard to match on any platform at any price