nor do all centers. And unless my math skills fail me, the hypothetical probabilities of getting on the all-star team as a center and as a defenseman would rise proportionally with the size of the league.
I don't know about that. Your math is right, but you're ignoring the fact that the best players will always be the best players, regardless of the size of the league.
Bourque would be Bourque in a 6, 12, 30, or 60 team league.