From reading what new units are introduced, the game seems to be more leaning on the "rock-paper-scissor" style gameplay(In terms of "resource comparison", for example, 2000 gold worth of Siege Engines being able to counter 6000 gold worth of Chimeras, Starcraft 1 had a smaller "resource gap" between unit counters).
In one of the Q&A batches, Karune described how he used one of the new units, the Jackal, managed to beat an entire army of Marines easily, (6v15) without losing a unit.
Not to mention the Immortals, which counter units with high damage but lose to low damage units. Warp Rays, which counter units with high health but lose against low health units.
You could say Scourges countered air units but they aren't fool-proof against air. It's not like you can mass scourges and expect to win against an army of air units(due to the fact most air units can be microed to kill the scourges), unlike WC3 which had Siege Engines, Gargoyles, Hippogryphs, Crypt Fields, Dryads(vs magic air units), etc which all either completely decimated air or were immune to air units(Dryads), Starcraft 1 doesn't have anything like that.
Closest thing was Firebat countered/decimated tier 1 lings and (but Firebats lose against upgraded lings), Defilers effective against all Terran units with plague, Psi Storm countered low health units(and effective against everything else), and Science Vessels effective against all Zerg units.
Last but not least, damage types and armor types which are being added to Starcraft 2(which are going to be similar to Warcraft 3's damage/armor types).
In Starcraft 1, the damage types were very simple, there was only 3 damage types and armor types: Explosive(100% to large units). Normal(100% to everything), and concussive(100% to small)(only firebats, vulture, and ghosts had this damage type).
In general, damage types simply meant that larger units were more balanced against smaller units, and concussive simply meant ghosts sucks, firebats are only good against zealots/lings, and vultures were good against small units but are mostly used for planting mines.
In general, Starcraft 2 seems more rock-paper-scissory to me. Basically, that means Starcraft 2 probably will require more of a "mix" of units rather than using most of the same units (for example, Medic and Marines can be used throughout the most of the game against Zerg, science vessels and maybe tanks were used later on).