It's a fashion and we are much likely influenced by what we see on movies. Every time we watch a movie or Tv program, we see different products like laptops (mostly from Mac), wrist-watches, mobile phones and all kind of other stuff.
Watches in Movies
Yes, you can see a watch in almost every movie. If you have seen Thomas Crown Affair then the movie clip where Thomas Crown looked at his watch when he was in the car was put there by famous brand called Jaeger-Lecoultre Reverso. Unfortunately the brand name could not be shown because Pierce Brosnan had an exclusive deal with Omega watches. Also, lots of other movies have watch scenes and there are more to come. Watch brands are becoming savvier about promotion and marketing.
Watches make actors more stylish and give them a real character because you will remember the characters by their styles and body language. Lots of actors have exclusive deals with famous watch brands like Omega, Breitling, Hamilton Rolex etc. who will wear their watches during the castings. It's a good way to promote a watch because people are paying attention to what actors wear and do.
Movies can order special watches
Lots of watches are being custom made for the movies. One of the watches that was designed specifically for films was done by Hamilton Watch Company. This watch with special design was used in movie "2001". It was never considered to go commercial because watch was just too complicated. But surprisingly, Hamilton Watch announced that it made the "2001" watch commercial in Limited Edition.
Also, action star Arnold Schwarzenegger who is now governor of California worn Audemars Piguet watches in his movies. For "End of Days", Audemars Piguet created special watch called the Royal Oak Offshore to be worn by Arnold Schwarzenegger.