If you type script/rails generate, the only RSpec generator you'll actually see is rspec:install. That's because RSpec is registered with Rails as the test framework, so whenever you generate application components like models, controllers, etc, RSpec specs are generated instead of Test::Unit tests.
Note that the generators are there to help you get started, but they are no substitute for writing your own examples, and they are only guaranteed to work out of the box for the default scenario (ActiveRecord + Webrat).