Although the cynic in me wants to say "Oh dear, already? Did she blow all her money in Vegas or something?"
Given that she's the first British billionaire to lose her billionaire status by charitable giving that's a little too cynical in my opinon.
Cynical and ignorant. I can be very efficient like that.

Seriously though, I think the source of my cynicism may have been that this is a direct to film project, not a new series of books, which to me usually spells "cash-in".
Also, I feel I need to stress that the bit you quotes was only a gut reaction--the rest of the post more was actually much more positive. Not to harp on but I feel I'm being quoted a bit out of context.
Terry Pratchett has done 30 or more Discworld novels, spin off books, games, interactive stuff, TV shows, etc. Yet seems to be universally loved. Is that not milking it?
Apples and oranges. Discworld is a world ("and mirror of worlds") while the Harry Potter books were centred on the "heroes journey" of one character. Since the world itself essentially revolved around him, it's still questionable (though by no means impossible) that it can find a life of it's own. By design, Discworld never had that problem.
Also, I tend to agree the Pratchett's writing ability is objectivity better. However, to be fair he's had *way* more practice and the quality has improved dramatically since the first three or four books. Which brings me to my next point: it's only "milking it" if the overall quality of the IP is compromised.
As a side note, I do recall reading something about Rowling being less than complimentary of her peers, and Pratchett being less than impressed with her. I think it had to do with her having a generally low opinion of fantasy literature in general, but I may be misremembering.