tf.variable_scope is an evolution of tf.name_scope to handle Variable reuse. As you noticed, it does more than tf.name_scope, so there is no real reason to use tf.name_scope: not surprisingly, a TF developper advises to just use tf.variable_scope.
My understanding for having tf.name_scope still lying around is that there are subtle incompatibilities in the behavior of those two, which invalidates tf.variable_scope as a drop-in replacement for tf.name_scope.
