[respond_with] Need comments for #5199 on rails.lighthouseapp.com

I look for the consideration of ticket of #5199 (https://
rails.lighthouseapp.com/projects/8994/tickets/5199-respond_with-
returns-on-put-and-delete-verb)

Most likely my questions are addressed to Jose Valim.

The fact is that I do completely understand the logic of the work of
respond_with. Especially, when the matter concerns the use of
respond_with for writing JSON API for my site.

Here are my questions:

1. Why respond_with reacts only on GET and POST verbs?
If, I change certain object in the model with the verb PUT, then I
desire to return the certain information.
For example, something like this (in the case of success)

  render :json => {:user => @user.id, :result => 0}

or

  render :json => {:user => @user.id, :result => 1}

in the case of the failure.

This is impossible either for PUT, or for DELETE. Thus I am forced to
forego render_with in favor of render.

2. For example, action answers on URL http://localhost:3000/send_email.json.
Why

  respond_with {:email => 'test@my.host.com', :status => 'Success!'}

returns nil, while

  respond_with [{:email => 'test@my.host.com', :status =>
'Success!'}]

does return correct JSON?

I hope that Jose and community will help to explain the situation.