Waldman explains:

If he were not as rigorous as he is but was producing the same results, liberals wouldn't be as taken with him as they are. There are Democratic polling outfits out there, and while liberal blogs might cite them fairly often, none of them have produced the same devotion Nate has. On the other hand, would liberals be as interested in Silver if his analysis consistently predicted a Romney win? Probably not.

In other words, it took both to make Silver a liberal hero. His projections had to make liberals feel optimistic, and he had to be going about things in the kind of nuanced, detailed way he is. Liberals are pleased as punch that the thing they want to be true can be supported by a highly complex and sophisticated analysis. They want to feel good, but they also want to feel smart.