That's the narrative terrain of the movie, and TRON Legacy explores it about as deeply and as meaningfully as one would desire from a high-tech, 3-D, action entertainment. Niggling complaints aside, this is a genre film featuring just about the right alchemical equation of thrills and heart.
The identical order of events -- and deliberately re-use of trademark franchise moments such as the disc battle, light-cycle race and beam-rider interlude -- suggest that this "Grid test," as it were, is actually symbolic. It's a rite of passage. First the Dad had to survive it, and now it is the son's turn to run the same gauntlet.
Since so much of TRON Legacy concerns the the son growing up, and (hopefully) avoiding the mistakes of his father, this narrative structure does not feel like a re-hash of the earlier film, but rather an important point of context. This is life, the broaching of adulthood and responsibility, the movie seems to intimate. And by putting our new hero, Sam through the same events his father endured -- and in the same order, no less --the film gets that point across rather nicely, and without forcing the issue.
The prime difference between original and sequel arises not in the order which the the action-packed events occur, but rather in the perspective in which how they are viewed. In the first film, Flynn attempted to survive in someone else's system.