I had thought the same thing when I first saw Colin Creevey during the battle however I read an interview today with Rowling herself and she answers that very question... here's the link MuggleNet | The ULTIMATE Harry Potter Site - Harry Potter and the Deathly Hallows, Harry Potter and the Order of the Phoenix, JK Rowling, rumors, news, forums, images, video, and more! its about half way down or there abouts. The rest of the interview is well worth the read anyway