The more complicated a game is, the longer it takes to develop. But all that time is not spent just on programming the game - which is actually pretty much the last thing you do, IIRC. Creating the story, characters & setting has to come first, then all the design work for concepts of locations, items, people etc. Only when all THAT is done does the programming part actually start.
So 'X years in development' does not equate tp 'X years of building the game engine' at all...
