The simple answer is yes ... and no!
Most of the big hit movies are to some degree 'star vehicles', but then there are plenty of counter examples too, from
Paranormal Activity to
Bridesmaids, or
Billy Elliot for that matter!
More and more films US and UK films are funded by pre-selling distribution rights to foreign markets, a strategy UK social realist filmmakers such as Ken Loach and Mike Leigh relied upon for most of their careers. In their case, they could pre-sell to European markets where they were held in very high regard as auteur filmmakers. More mainstream films, even at the low budget level, will frequently encounter foreign distributors demanding the presence of some star with appeal in their territory, reinforcing the position of stars as vital to a film's prospects even if the evidence of success is very questionable.
At the tentpole level there is also a yes and no answer: big name stars with wide international crossover appeal help sell the movie, and their appearances on major TV shows across different territories/markets, their presence at red-carpet openings, usually helps generate buzz. However, technology can be just as big a factor:
Avatar wasn't reliant on big names but rather the combination of groundbreaking CGI/SFX and the brand of director James Cameron, just as Michael Bay's name and the associated guarantee of lots of spectacular explosions that the producer of such successful bilge as the
Transformers franchise brings is at least as important as any star name attached.
Here's a few links for further reading on this - useful for reflecting on your own target audience too.
Michael Bay gets narked at Transformers star slagging off the movie!
After enduring the unenthused gripes of his two leads, Shia LaBeouf and
Megan Fox, Bay has apparently been forced to his breaking point by the recent comments from Hugo Weaving, who called his voice-acting gig as Transformers villain Megatron a "meaningless" job that he "didn't care about."
EC McMullen Jr gets rather cross at the very idea that stars sell pictures, specifically horror...
Two major factors will sell your genre movie to the fans. One is someone and something they've never seen before (so if you're dry-humping NIGHT OF THE LIVING DEAD, ALIEN, or SAW, you lose). Two is fan recognition. Fans are more apt to go to a movie made by a director, writer, or producer (even a freaking