I think this was the original wart that started the whole WSGI 2.0 process. As I recall, it was PJE himself who recommended dropping start_response and replacing it with a return tuple of (status, headers, iterable). PJE comments in one thread that this isn't a reduction in features, but an improvement in usability:

"Note that in the WSGI 2 calling protocol, you would simply modify your return values, rather than needing to create a function and pass it down the call chain."

http://mail.python.org/pipermail/web-sig/2009-November/00424...

Here is an example of a thread where it's discussed: http://mail.python.org/pipermail/web-sig/2009-November/threa...