The difference (or at least part of the difference) is that Ferrell had no hand in the writing or producing of Blades, as he did on Anchorman and Talladega Nights, and the paycheck-cashing nature of his performance is pretty apparent. It doesn't help that he's acting opposite Heder, a one-note actor if ever there was one, as Jimmy MacElroy, Chazz's fey rival-turned-partner thanks to a skating-bylaws loophole that allows them to compete as a pair even after they've been banned from singles competition after a nasty fistfight.
So it's Ricky Bobby and Napoleon Dynamite on skates, with exactly one joke for the whole movie: Figure skating sure is gay, isn't it? As Chazz and Jimmy learn to put aside their differences and work as a team so they can defeat a champion brother-sister pair (Arnett and Poehler), there are many, many moments of awkwardness as certain body parts come into uncomfortable (and supposedly hilarious) contact with certain other body parts. This is a movie built entirely on gay panic.
And when the gay jokes stop as the movie builds to the inevitable (and predictable) showdown, suddenly there are barely any jokes at all. Ferrell runs around in his underwear and sings "My Humps," but the movie never has the manic energy or creativity of Anchorman or Talladega Nights, and despite the many cameos from skating stars, its only function is to engage in facile mockery. And, of course, to score some easy money for Will Ferrell.