Neither 3e nor 4e started life by coming out with a basic beginner box first. Maybe that's why neither edition seems to have had the traction in bringing in new blood that stuck with the game. (The part about new blood is my guess, feel free to disagree.) Keep on the Borderlands was one of the top selling modules, if not the top selling module because it was included in the Basic Boxed set. This indicates how the Basic set was a top seller for TSR.
Another benefit of coming out with a starter box first is that we the players will have the initial kernel of the game to play with while the developers fine-tune the rest of the core game. Advanced options such as epic level play can be left out of the second book or books so they can be brought to market sooner instead of having to wait for a reasonably developed set of rules for high level play.
Once they have the more basic "core" elements of the game ready to publish, they can move on to the next click on the complexity dial. This is how they can implement modularity so the game supports more or different levels of play.
Another benefit of coming out with a starter box first is that we the players will have the initial kernel of the game to play with while the developers fine-tune the rest of the core game. Advanced options such as epic level play can be left out of the second book or books so they can be brought to market sooner instead of having to wait for a reasonably developed set of rules for high level play.
Once they have the more basic "core" elements of the game ready to publish, they can move on to the next click on the complexity dial. This is how they can implement modularity so the game supports more or different levels of play.