The sales figures do not seem to bear that interpretation out. S_D is unique in their widespread distaste for much of the Marvel line; many other comics forums are nigh-united in their belief that, overall, the quality level of Marvel's output right now is actually quite high.
Good writers are putting out well-drawn comics: Ultimate Spider-Man, Dark Avengers, Jason Aaron on Wolverine: Weapon X, Whedon and now Ellis's delay-plagued Astonishing X-Men, Jeff Parker's Agents of Atlas, Greg Pak and Fred Van Lente on Hercules and Hulk, Secret Warriors, post-Ennis Punisher MAX, Immortal Iron Fist, etc. There are certainly low points, such as Ultimatum, but Marvel is currently doing quite well for itself on average.
When I read, for example, the comics forum on Something Awful, it's difficult to believe that they and S_D are discussing the same comic books.