Some of the differences between those two and COH is that they don't have "super" units (other than WC3's heroes)
Mothership is the only "real" super unit. But then you also have plenty of lategame units: Carriers, Battlecruisers, Broodlords. Up to some point Collusus and Ultralisk.
While talking bout SC2, you need to remember: Huge player base + only 1v1 balance mentality + mirror matches
This leaves you with balancing only for: TvP, TvZ, PvZ.
Here we have: OHvSU, OHvsUSF, OHvB, OKWvSU, OKWvUSF, OKWvB. You could say they also have to "balance" the mirror matches but...
...We care about teamgames also here. Just with 2v2 think about the amount of combinations.
WAIT, theres more. We have on the new factions 6 commanders which change gameplay completely while the vcoh2 factions have over 10 commanders. All which change completely the dynamic of each faction. Yep, easy.
You think we are done? Nope, we also have assymetrical maps!