343i isn't completely made up of Bungie vets but definitly Halo vets. All of these people are passionate about the series and they love coming to work to expand upon an awesome franchise that defines FPS games. They know they are the sh!t right now.
The new guys don't thank their lucky stars every day becausethey landed a job in a company that is developing a Halo game, they came to 343i for Halo. They arnt doing this for there resume. They people doing it for that left a long time ago.
343i probably have a test in there aplications that asks questions pertaining to the series so they know if they are hiringa fan or just some aspiring developer looking for a job. They hire the fans because they know what the fans want. The next three Halo games are going to be different from the previous but will include pieces of everything that makes Halo great.