I think it's an interesting debate about the nature and value of content. I'm a hack - I get paid for writing (and commissioning and editing). I disapprove of Huffpost and publishers who expect people to write for free. Ariana Huffington doesn't work for free, why should the people who provide her content?
However, being interviewed about your work can be different. I have been interviewed by national broadcasters about articles I've written - have only ever been offered a fee by the Beeb. BUT I was an employee of my publisher so broadcast interviews were part of my job and I didn't expect payment (and didn't take any from the Beeb). Equally I know some of the other interviewees were freelance and treated as 'contributors' who did get paid.
With a webchat the question is, who is providing the content - the interviewee or the posters asking questions? Or both? And who, if anyone, should get paid? If the interviewee is promoting a book, or a show, then clearly they are getting some value and don't get paid, any more than I pay high profile people when I interview them. But is the webchat interviewee a 'contributor' akin to a broadcast interviewee who is paid - e.g. a guest reviewing the papers on Newsnight?