It's actually more than just advertising Deathatthedoor, it's about your publisher, your agent, product placement etc. I have nothing particular against J K Rowling, I have never read the books, and probably never will, although I've seen the first two films. There are definitely children's fantasy authors like Diana Wynn Jones and Ursula K. Le Guin whose books should have got the attention that the Potter books have received (in my opinion). But it was a case of the right thing coming along at the right time. Having said that, Potter mania has helped boosted children's fantasy book sales in general, and also adult ones I believe, which can't be a bad thing.