This is true. However, since this is a problem which is literally encountered on a daily basis, I think a more general version of it might be important enough to merit the use of this technique. For instance, if the grandparent were reformulated as "please help me come up with an algorithm for what I should eat for breakfast in the future", then by devising a good one we could ensure that the questioner would no longer need to spend time thinking about his/her breakfast choices for the rest of their life while still being confident that they weren't suffering undesirable opportunity costs present in the "always eat Cornflakes" strategy.