Even if discworld is a bit over merchandised, so what ? I mean it doesn't change the fact that it is still a fantastic series of books and the merchandising is not stopping anyone from enjoying them. I mean star wars, star trek or lord of the rings are all over merchandised but that doesn't change the fact that they are still very good entertainment. So even if Pratchett wants to make an extra buck off his creation, I personally don't grudge him that. And for the true discworld nut, its just a way of getting closer to his passion, so everybody wins
.