Jason Silverman's take on Hollywood SF movies is that they're too laden with expensive effects to get greenlighted. He points to the recent failure of The Fountain, and morosely concludes that Hollywood just isn't willing to do big-budget SF films like 2001 and Star Wars any more. Not that they were actually all that willing back in the day, either; somewhere in my stacks of stuff I have a copy of the MidAmericon (1976 Worldcon in Kansas City) progress report which contained a notice that some filmmaker by the name of George Lucas was bringing a rough cut of his upcoming SF film to the convention and would be selling props to try and raise money to complete production.
The thing about this article that bothers me is that Silverman doesn't seem to be very familiar with SF or with the history of the genre on video. Some of the most God-awful dreck Hollywood ever made has been SF that had a ton of money spent on FX, while some of the most excellent SF movies spent a lot more time on plot and character while not being real big on the FX. By the same token, the BBC has a long history of producing excellent SF series with laughably minimal FX budgets (Dr. Who being perhaps the best known) that have attracted sizable fan communities throughout the Anglosphere and beyond. So it's not that it can't be done; it's that Hollywood doesn't seem willing to give it a try. There are dozens of award-winning and popular SF stories that wouldn't require much in the way of FX; The Stars My Destination, for example, is a Bruce Willis vehicle waiting to happen, and could be very cheaply done since most of the action takes place on an Earth not too much advanced (technologically) from the one we're living in.
I got to this article by way of a post in Ed Driscoll's blog which notes that while making small-budget "indie" films that don't have to play in Peoria to be successful might work in a purely bottom-line sort of way, in the long term (and it won't be a very long term, either) that kind of filmmaking is going to destroy the infrastructure needed to make big-budget blockbusters. Ed doesn't say it, but essentially what they're doing at the major studios is voluntarily retreating to a 1950s B-movie mode of production.