Actually these is quite a big difference.

PUT specifies the resource to be update, whilst POST does not do so. This means that you must (according to RFC 2616) use POST if you want to create a new resource and PUT if you want to change an existing resource or create one that you know "how to name". This disctinction is sometimes necessary, or at least useful (ex: idempotence of PUT).

I don't understand how any even half-competent developer would be unable to understand this difference and act accordingly.