By Brian Howard and James Sturdivant I own a Nook Simple Touch. Maybe it's because I root for underdogs or maybe it's because I chafe at platform lock-in and proprietary file formats, but I've been quite happy with life on the B&N ebook platform. Then, on Friday, Amazon announced its Stephen King Kindle Single exclusive, "Guns." In the short essay, King, whose book Rage had been linked to several instances of school violence, weighs in on the gun control issue. (King penned Rage as a high schooler. The book was published under his Richard Bachman pseudonym and has since been taken out of print  at the author's request.) I forked over the 99...