Once your code base gets to a certain size, the feature set gets big enough, and the maintenance starts stacking up, you need a more robust language.

Sure, plenty of web apps can run fine on Ruby, but even then, many of them start looking towards a language thats easier to maintain.

Good developers can move fast in Java, bad developers will move slow and screw up, even in Ruby.

Obviously, every Java project with hundreds of thousands lines of code can be written by 2 developers in Ruby in a weekend ;)

Possibly. But I'd like to see that proven.