By that reasoning, in Problem 2 the fact that one child is a boy cannot affect the sex of his sibling so you can reduce Problem 2 to Problem 1. The point that Norvig is making is that there are other reasonable interpretations corresponding to different sample spaces (and therefore to other probabilities).
But if your sample space is just Cartesian of {B,G} and {1,2,3,4,5,6,7} then it is in fact just a noise. If you had some additional information, that, say, on Tuesdays there are two times as much boys born as girls, only then expanding sample space would make sense.
Also, for interpretation of problem 2a there is one fundamental flaw that I can see: The sample space listed as:'BB', 'BG', 'GB' is wrong, because 'BG' and 'GB' are in fact the same sample. Or, to put it in a different way: if you decide that ordering does not matter then you should list either 'BG' or 'GB', not both. And if order does matter then you should list 'BB' twice, for all the possible orderings. Both of which will make probability equal to 1/2.
EDIT: Moral of the story is: "If it looks like paradox you are doing it wrong". Which I think was the Norvig's point from the start.
"The sample space listed as:'BB', 'BG', 'GB' is wrong, because 'BG' and 'GB' are in fact the same sample."
Flip two coins. Exclude the case where both are tails. What is the probability the two coins are different? If 'BG' and 'GB' are "the same sample", is it also the case that 'HT' and 'TH' are the same sample?
