the only thing i like about stores of all sorts that have only 1 brand is that if they are biased toward a model it tends to be for the right reason. For instance if a store carries Bianchi and Giant, there may be 2 bikes of a comparable price but the person might not push toward the right bike they may (hypothetically because i have no clue of the mark up) push you toward the Giant because they get 35% profit on it opposed to the Bianchi that they get 25% profit, when the bianchi may be a slightly better bike or just a better bike for you. Thats the only thing i like about stores with an exclusive contract with one brand, of course that is assuming that it's a brand that you like. I would however prefer a store with more variety, but i'm just pointing out that when a store carries only one brand there is at least one good point to it.
kyle
i have known places(not bike shops) that would push a certain brand although it was an inferior product just due to it being a higher profit margin, but hey, that's business.