Truth be told, your students are pretty smart to focus more on sales and adaptability. At this point, there are infinite possibilities as far as production phases -- some games go through dozens and dozens of phases, while most (I would say) are released after less than half a dozen phases. Some are produced in just two (a broad "development" phase, which I lump into a single phase, as everything can be completed by one person, in one place, with no changes in supplies or requirements -- and "distribution" phase... which can be as simple as uploading your game on a website).
Then again, if your assignment is intended to be comprehensive, and examine all the possibilities, and examine case studies of various production methods... the students who chose to write papers on the video game industry are nuts. Ha!