It is true that some brony stereotypes may in fact have some truth to them. However they are often exaggerated, only imply to some or are made out to be a bad thing. For example A large amount of the fandom do in fact have autism (including myself) is this a bad thing? No, not at all. Satoshi Tajiri, best known for the creation of Pokémon had autism. Even people like Elbert Einstein also had autism. In this case what is so bad about "autism anyway"
Bronies spend most of their life on the PC: I guess this has more to do with the person you are referring to rather than a fandom, I also tend to fall into this category, I guess I'm just more of a introverted person. But that's me, not every brony out there. Besides it's not exactly a bad thing anyway. It all comes down to preference.
Generally many stereotypes, are unreasonable and exaggerated.