I do not understand, why they are overcomplicating things so much - why isn´t there just ONE rails framework? Issues with backwards compatibility vs. new features? Or what was causing this "forks"? In three years, will there be six rails versions?
The 3 versions patched are not forks. They're just different versions of Rails. In three years, they'll probably still support about 3 versions and drop support for older versions once they hit a certain age.
You can find the exact maintenance policy here: http://weblog.rubyonrails.org/2013/2/24/maintenance-policy-f...
You can check the upgrading guide for more details about what's changed, and a third party is selling an ebook that has a ton of good info as well.
We're also starting to use verb-matchers in the routes file, but that's going to be a bit more painful to deal with…