1) Apache supports MANY server side scripting languages, and PHP is just one of the many. Look at mod_perl, ColdFusion, JSP (via tomcat) or even server side includes or FastCGI C++ programs.
2) Apache supports nearly every server platform there is. However, it is primarily aimed at Unix and Unix like operating systems. I.e. HPUX, Solaris, AIX, Linux, BSD, etc...
3) Apache is NOT the fastest web server there is. It is, however, very functionally correct, and very stable and reliable. you won't spend day after day trying to figure out why something that should work isn't working. It's easy to configure, once you understand the syntax of the httpd.conf file and read up a little on it. It's very cheap (free is hard to beat) and very versatile.
Finally, no one can stop supporting it. It's open source, so you don't have to worry about the company that makes it withdrawing it from the market some day and your not being able to get updates.