How do you think they pay for some of these movies? Ever notice back in the day, that all the cars in a movie were made by one company ( well, the ones involved in the scene anyway )
Product placement. Used to be that you would see generic stuff like pop cans, but now you see people sucking on a Dew, etc. Kinda nice because it makes the scene a little more realistic.
I'd love to see an Alienware computer stuffed in a scene of the next Matrix movie though