I guess that's the thing, if Paul was winging it but has a great deal of experience doing the same thing, that's totally different from Joe Random turning up at a (paid-for) conference without slides or script and saying 'Er, well, I didn't prepare...'. Unless Joe Random is a celebrity of some sort, people will get pissed off.

As a total aside, winging it can be great. I far prefer that style to people who are clearly reading from a script of sorts. My performance background's in improv so I'm biased, but I strongly recommend anyone who wants to take up public speaking spend some time in improv workshops. Once you can structure a longform narrative from nothing but a word shouted by an audience member, giving a talk is easy.