Exactly.
Verizon Wireless puts games on most, if not all "multimedia phones" in the hopes the consumer will love the game demo so much they will pay extra to download.
I recently purchased a BlackBerry Curve 8530 and noticed the Sims 3 is preloaded on my phone as well. However, I do have a data plan, and would probably be able to download the full version of the game.
Either way, games eat up a lot of memory and battery, so it may not be the best idea for you to play the demo too often.