If we look at a lot of big budget movies today they are fine without celebs. Heck JJ Abrams told Matt Damon he does not want him as Kirk. Avatar did fine without a major star, so did a bunch of superhero movies. Are the stars fading?
The star power would be there but good films with good stories can still make without a big star, which is good as at the end of the day it should be about the art and not just eye-candies.
Word. Avatar had a number of known faces. No, you don't need Denzel or someone in the film, but you generally need a familiar face to help connect people to it.
I would have gone to see Prometheus regardless, but Madame Theron definitely helped to get me in the seat.