I'm sure it is possible they are doing it as well, but I was talking about what I saw on twitter's new design. I don't use Facebook, so it was definitely Twitter I saw. This was a while back, so potentially it isn't the case any more.
I'm a little new to this but my understanding is that that would be the same as doing a GET request to the REST API. Which would have the same penalty for going over 30 req/s without an OAuth token.
For example, this is what my get request to the REST endpoint looks like without URL parameters:
GET reddit.com/r/explainlikeimfive/comments/2w1xzo.json
Which returns the same response as appending .json to the the URL: