I think the "long tail" of shared hosting providers use CPanel, with no support for ruby. Including Ruby in CPanel means every Linux host will be able to offer it, and it also means that Ruby on Rails will become a standard, the same way PHP is. That's a huge difference from where Rails is at today. Most won't deploy it, but having built-in support for Perl, PHP, and Rails shows just how important the language is, even though most people outside startups don't use it currently.
Although, if somebody just wants a quick script, they will probably use PHP. Ruby on Rails is more for somebody who wants to create an entire database driven web-based application. So, maybe Ruby on Rails is a niche. What do you think?