I think Ruby on Rails default scaffolding actions and routing have influenced the popularity of the half-REST design.
I myself have been guilty of this. At the end of the day, supporting PUT at expense to ease of use by the API consumer (and effort expended to support their toolchains and SDKs, most of which need extra twiddling to do PUT and DELETE) is just not preferable to getting something working... REST philosophies be damned.
http://www.phpbuilder.com/manual/en/features.file-upload.put...