Is this fear of R ratings a recent thing? I don't remember Hollywood people having such a problem with R ratings before the last 5 years or so. Does it really hurt a movie's box office that badly if it's R?
It's more that sci-fi films, in addition to being comparatively expensive, are already a niche market segment (there's a reason the ads have been playing up that Scott is the director of Blade Runner and Gladiator, not Alien), and R-rated films, generally speaking, don't make nearly as much bank as their lesser-rated counterparts. Of the top twenty grossing films in 2011, only two -- The Hangover Part II
-- were R-rated, and those were comedies with broad audience appeal. An R-rated science fiction / body horror film is considered less likely to be a box-office success.