This is the one thing that allows SC and WC to remain somewhat different games while still both being RTSs. In WC3 a skilled player would only need a handfull of units to do considerable damage. However it required a lot of micro and spell casting. The hero being a big piece in that. SC on the other hand, esp at the end of longer games, requires less micro of your armies since both teams are just pumping out massive armies and sending them to fight. In the gameplay video the guy notes that SC2 is still about large armies just as the first one. The mothership is the closest thing to a hero we will see as far as abilities. I can almost guarantee you we won't see actual heroes similar to wc3. To be actually be usefull against large armies and be worth having they would have to pack quite a punch.