ok found the issue, this:
// Build GET expression
strRequest << F("GET ") << MY_SERVER_GET_URL << F("?count=") << iLoopCounter
<< F(" HTTP/1.0") << "\n"
<< F("Host: ") << MY_SERVER_GET << "\n"
<< F("Connection: close") << "\n"
// send data via request
// close connection
is not a true or correct GET request (I don't know which it is or why and I would quite like to know why). So my php check for the GET request was failing:
if ($_SERVER['REQUEST_METHOD'] == 'GET')
It didn't fail through the browser, command line or my Max/MSP tests as they are all true GET requests. The request string is almost identical to the one in the WebClientGetPost example that comes with WiFly (I just changed the variable and value) so that must be wrong as it's normal to check php side if it's a GET or POST request (amongst some other checks to see if the request originates from the right source).
Thanks for all your help and patience pylon, this I think has been technically the most gruelling thing I've ever done.