It seems many hosting companies or their sysadmins don't agree since PHP gets installed and Ruby, etc. doesn't. PHP is an easy to install module and very easy to do the first program since its just a part of the webpage.
If you want your favorite language to replace PHP, then you have to make it easy for the sysadmin to install (preferably 1 line) and for new programmers to be able to use the language by just uploading a file.
Yeah, but PHP use as CGI was likely never more than 1% of the market. What most people mean is installing mod_php is easier than setting up another language via cgi or fastcgi.
That's really just not true. Installing anything capable of CGI is as easy to install as PHP.