Studios are risk averse. The last thing they want is someone with a twitter following trouncing their film. Thing is though, most of the tweeters above make a living from the entertainment industry, thrive on access and would never dream of upsetting anyone. Give people a few drinks, show them some cool stuff and feed their need to feel important, and hey-presto: lots of positive tweets, even if the film sucks, because you want to be invited to the next one. Simples.