rails/rails — comment on commit dad7fdc5734a3813246f238ac5760b2076932216
File:  line 0
By pavelvasev:

Dear Spastorino, thank you for fast reply!

The link you provide shows only one explanation: "vendor/plugins/* were on their way out with Rails 3.0, moving to gems instead. This is their last hurrah."

So actually we still have unanswered question - why plugins are moving out from Rails?