Could Ruby on Rails have been created in another language like PHP, or are there some functions in the Ruby language that make the difference?
Rails makes heavy use of Ruby's ability to dynamically add classes and methods—there are implementations of similar frameworks in other languages, see Grails as an example. Other languages that provide a dynamic class runtime could be used, such as Smalltalk or Objective-C. In fact, Rails has a lot of similarities to the earlier, Objective-C (and Java) based WebObjects web application framework.
There aren't many things that one could do in Ruby more than in other languages - certainly Python is pretty similar in general and since Rails was released many other languages have implemented a railsalike framework from direct ports to tools like ASP.Net MVC.
What was different about Rails when it came out was the conceptual jump that lead to a framework that did so much of the basic legwork for you but left everything easily changed and kept out of your way once it was working. That kind of thinking is something that you might expect to come from the Ruby community because Ruby itself is designed to be very developer-friendly. It was that philosophy extended to web development that was the foundation for the Rails platform.