XS requires a C compiler. Hence, most Win32 users (and many Unix users, believe it or not) cannot use modules that have an XS component directly from CPAN.

I'm facing this issue right now at work trying to get a clean system up for a webserver in a DMZ. My dev box has all the tools, so I built a bunch of stuff. Now, trying to get those same items over into the clean box without accidentally polluting it isn't so easy.