The more units thing is part of the reason I think Dota is a better challenge, I can't help but feel a SC2 AI could use inhuman micro as a crutch whereas in Dota mechanical / micro skill doesn't provide quite as big an advantage.

Not too sure what you mean by 'rushes can be punitive' but Dota certainly has a variety of early game aggression strats which tend to be high risk / reward and are seen fairly regularly.