Data that is posted to PHP via the PUT method is not parsed at all and is not available to PHP. This is particularly problematic for data sent encoded as 'multipart/form-data'. [...] This is something that would help every RESTful interface that people are trying to do with PHP. There are many people who have these problems and have to implement (usually incomplete and/or buggy) PHP solutions.
In the Reddit post there's a mixed set of opinions - some say that things work well enough as is (content pulled from the raw stream) and others say that adding something like this makes the HTTP support more complete and functional.