i bet a lot of the budget for the majority of games is advertising and publishing costs
i bet man power makes up a large chunk of the budget

indie games generally have less ppl working on them, and the ones that are working on them, can do it in thier spare time.
so essenially they can creating them for free.
development teams for some of the larger games, could be 100's of people.
say you have a small team of 20 working on a game over the course of 3 years of development, and are getting paid an average of say £25,000.
that still comes to £1.5million, just on wages for a small team