AJAX supported browsers and operating systems

I'm really confused about the supported browsers and operating systems for AJAX. As stated here:

http://ajax.asp.net/docs/BrowserCompatibilityForASPNETAJAX.aspx

It says that AJAX only works in XP (SP2), Vista, and OSX (intel only). Why is that?

I thought this AJAX stuff was just generating javascript so what does the operating system matter? If it works in Firefox on Windows then surely it should work in Firefox on Linux and Mac as well. And why Intel only Macs? It can't be making calls at the machine code level so what does the underlying hardware architecture have to do with anything?

Can anyone shed some light on this for me?

Thanks, Dave.

They may not list Linux because there are a LOT of different distributions out that and it might not work for 100% of the setups. I have tested some of what we have done on my laptop with Ubuntu 6.10, and most stuff worked the same. Really the only problem is that Firefox on Windows renders things slightly different than Firefox on Ubuntu. Some menus ran over, but generally it functioned about the same as firefox on windows.