Do Ты think the Twilight Stars's personal life played a key-role in the movie's so-called success?

I think it's moreso the other way around. Nobody cared much about them until they were casted for Twilight movies.
People were into Twilight and the idea of a movie before anyone was casted.

I'm sure it contributes some, but the people who are into Robsten are major Twilight Фаны anyways, so I don't think it has that much of an effect.
Some other Фаны don't even like the casting.

(There are a lot of people who watch a lot of Фильмы just for the casting. I'm sure there are a lot of people here who watched "The Woman In Black", that Ballet Slipper movie, and "Cherrybomb" just because of specific cast members.)