In StarCraft 2, are points comparable across leagues?

The short answer is: Points are not Comparable across leagues.

The accumulation of points is supposed to be proportional to the difference in skill between players. Unfortunately, the points you gain are unrelated to your ELO style rank. Because of things like: Bonus points, starting off at 0 points, and league promotion devaluing points, points don't correspond to a true ranking.

Instead, sites like SC2Rankings and Starcraft.org realize that the hidden ELO style rank that Blizzard uses is only accurately reflected in promotion between leagues. As a result, the best indicator of skill is what league a player is in. Since points are comparable inside of a league, the secondary sort these sites often use is that point metric (despite its deep flaws).

I'll probably write a longer explanation of how an ELO style ranking system should work to highlight why points don't, but the bottom line is still going to be: points aren't comparable between leagues.