Firefox runs on Windows and MacOSX too, if you haven't noticed...
Way to miss the point. Unless you're stealing Windows or MacOSX, neither run Firefox for free. And my point about Firefox is that the applications people rely on are increasingly becoming web based, to the point that the operating system matters much less. At that point, nobody wants to spend money on something that's no different to a free something.
As for PPTX, OpenOffice 3 handles that fine. It handles doc, docx, xls, xlsx, whatever else you want to throw at it, and it's free. Plus the interface sucks way less than the latest Office one.
As for people wanting to use Photoshop, can you honestly tell me someone who spends $500 on a PC is going to spend $500 on an image editor?
This topic seems to have turned into the usual poo flinging with the usual trolls, so I'm done.