Hadn't noticed, but I'm not surprised. . . Cook and Hall actually have a very wide range of selling prices across sets.
All of these artists (and many more) are fantastic, but there are only so many collector dollars to go around -- especially on the high end cards. When just a few collectors stop (or start for that matter) buying it can impact the prices dramatically.
Chicago Comic Con 2013 Review. . .
Plus: Card News, Interviews, Trade lists, galleries, show reviews and various non-sport card stuff.