I'm pretty certain they had to build a completely new engine and like Brad says, that takes alot of time.
Then they messed around with alot of unitdesigns. They scrapped some, changed some and completely overhauled some (I've followed it since the announcement in May 2007) and some they messed around with for a long time before scrapping.
And they're still not done! The Zerg Lurker isn't in the beta and they just recently changed abilities like the Nexus speed/research aura and removed the Obelisk/Dark Pylon. Then we got the Zerg Queen which they're messed around with a whole lot....just waiting for someone to find the current big imbalance that will dominate....will probably 24h or so ^^
I'm sure they will fix and add stuff in the two expansions. But that's simply what we have to put up with if we want a competetive game which have three completely diverse races.
The zoom is that way since it's an e-sport game where people have to have identical settings (I don't completely agree with that) and also since Blizzard think it's the best way. E-sport games have to be spectatorfriendly and Supreme Commander I think is "too big" while Sins is just macro and have no rewarding micromanagement.
And watching from a players perspective in SupCom is just lol since if he zooms out to max like one great player did then it's just a bunch of dots....who on earth would want to watch such a match..? And how immersive is it to play like that??