1) I've never gotten much utility out of Rails books. I've generally gotten much more use out of the API docs and blogs. That said, the Agile Web Development with Rails book is pretty much standard, and Rails Recipes is good for code examples. However, if you're doing something in Rails Recipes, there's probably a plugin for it by now.

2) Because it is very easy to implement an idea in a day and see if it sticks. More than that, when you're faced with a task that might not have much reward, it is easier to do if it doesn't feel like work. Programming in PHP/Java/C#/etc generally feels like work. Programming in Ruby generally feels like fun.