" Blizzard pledged "never again" but somehow I doubt that they'll stick to that pledge if it threatens them with any real opportunity costs."
You're overreacting. Blizz did stick to this pledge and there is nothing to point to the fact that they won't here. My Mac client patched just fine, so did a friend's. Do they have bugs to iron out in the mac client? Sure, but patching issues aren't a huge deal. They have 3 months to fix them. There were patching issues in the Windows client earlier as well, these got sorted out. I see nothing in the Mac beta that makes me think they won't reach launch on time.
"and reading the beta forums one is left with impression that there are still severe balance issues between races."
People tend to shout "imba" when they lose and can't figure out a proper counter. The problem with balancing a game like SC is that so much of the actual game balance comes out in the metagame, and this takes time. SC:BW hasn't been changed in, what, 7 years? And yet the way the game is played today is totally different than 7 years ago. What was once thought was OP is now not a big deal, people figured out how to stop it. If you keep mucking with units and balance, you never have the opportunity to see if the player base will "learn" how to counter challenges on its own.