Is that because you think Macintosh and Linux users don’t want to give to charity? Is it because you are unaware of the other, more secure browsers available? Or maybe you’ve signed a deal with Microsoft to use their audio file format rather than one of the many other formats available.
The advantages of web standards are clear to see; for example consider that the HTML code of my version of your page weighs in at a fraction the size of your HTML code. That may save you a considerable amount in bandwidth charges when applied across your whole site.
Whatever the reason for the decision to not build your websites using international standards, I’m disappointed and it’s made me have difficulties in using your site. Surely it’s in your interest to make your website as open as possible, so as many people as possible can use it and help to fund your excellent work. I firmly believe that web standards are the way forward to ensure a more open, accessible and scalable future for the web.