From my perspective, it also looks like one book was just sort of "meh, I guess we have to do one of these" versus "ooh, you know what would be really cool to do?"
Lots of subjects have been covered many times, in many mediums, but someone fired up about a project can still do something great with it. How many comic books has Batman been in, for instance? And yet, every year, there's at least one truly great new Batman story.
Yeah, giants have been covered a lot less, but dragons are freaking Batman. It's always possible to do something awesome with Batman.