They aren't blocked by law, they are blocked by patent. Photoshop is nearly a decade ahead of Gimp at the professional level. In fact Adobe Elements is probably better than most of what the Gimp can do. Lets be honest, Adobe has spent multiple billions developing Photoshop over more than 2 decades. It's going to be quite a while before FOSS software can match that kind of commercial investment and support. Until someone that wants to be a competitor to Pantone and Adobe that is developing FOSS software steps forward I personally don't think the gimp could ever catch photoshop. Photoshop has a near monopoly in commercial publishing and Pantone does have one in color. Combined that's something that's almost as difficult as the MS monopoly to crack.