sharing art assets is a bad idea, the last thing we need is games which look the same. Which is why I said that the graphic engine is one of those things studios can have a 1 time to creat fee but after that it pays for it's self which each games that is made on it, after that they can have a smaller team working on the engine to continue refining it...consider it like maintenance, a Good example as well is capcom with their FramWork engine, now it's up to version 2.
Most time is spent on art assets because this is what make a game look district and give it that vibe that goes along with the atmosphere of the game, but the expense comes from hiring a shit load of people, just take Ubi's SC:conviction or Assasins creed 2, something like 400 people each, each one has a wage, so it's the man power which is costing them, the way to reduce people is to have efficient tools like others mentioned as well as having very skilled and talented people whom are multi-skilled as much as possible so that work is done efficiently.







