The rise of Rails has one story that's more important than any other. The story of blending. Blending mind, talent, and passion from widely different cultures across the entire complexity scale of software development.
It's a story about building a community consisting of seasoned J2EE developers responsible for making banks and the rest of the corporate world run on time. And at the same time inhabited by graphical designers pushing the envelope in look'n'feel who are just starting out in programming. And every single step in between.
That's remarkable. The J2EE guys would probably never have felt passion for doing Cold Fusion or PHP or any of the other technologies that normally appeals to designers turning into programming. And likewise, the designers would run screaming away if dumped in the backyard of J2EE. But Ruby on Rails is turning out to be that place in the middle capable of igniting excitement from both ends of the spectrum.
Why is that? I think part of the reason is that a lot of interesting properties around technology are universal in their appeal. Getting started quickly and feeling success early appeals to everyone (perhaps more critically to newcomers than veterans). Seeing the rise of beautiful coding structures arising from elegant syntax and the adherence to DRY (something that should be more appealing to the veterans as they've seen the consequences of the opposite). So what we're basically trying to achieve is the meeting of quick'n'dirty with slow-but-clean into quick'n'clean.
Now that the place in the middle exists, we're seeing the results of combining vast experience in enterprise systems with dedicated attention to look, feel, and eye candy. This is infecting both sides with the opposite concerns. The designers learn to appreciate abstraction through encapsulation and coherence much earlier than otherwise. The back-end programmers learn to appreciate and build consistent, accessible interfaces.
And Rails benefits enormously from the ideas and implementations steeming from both camps. From optimic locking strategies on the one side to Ajax visual effects on the other. The vision to address the full stack of web development makes ample room to include everyone.
See also ThoughtWorker and J2EE developer Obie's take on many of the same perspectives.