In reality someone would have had to bake the pie, and it's fair that they get it since they put in the work. The problem is that the author, in creating the example, eliminated certain facts such as the baker in order to get to the essence of the problem. But the more facts you eliminate the more chance that something will appear arbitrary, due to fewer paths back to reality. It's the fallacy of the over-simplified model (no that's not a real fallacy :).