SC is the Quake3 Tourney of RTS. Solid game that requires reflexes as a primary 'skill'.
SC also has a huge player base and battle.net and they had it really early on too. A lot of games like AOE were awesome but connecting to other players was a pain and you were pretty much limited to playing your friends.
And yea, SC does cut a lot of features like formations. It just requires the player to make up with apm which is where micro comes in. Most other games are not as apm intensive. That sort of just makes SC more fast paced and focused on low leveled basic functions.
Stuff like mass void rays aren't necessarily countered by units, they can be easily countered by proper scouting and a well timed attack. A mass army of voidrays would also probably lose to a pure marine army of the same cost, the difference being that the marine army will be on the field well before the voidray army is completed and can be replaced much faster.
And by controllable units I mean by how units fighting each other win based on the player's skill, not just on their stats. A lot of units are extremely effective counters only if you know how to use them. For instance, vultures counter zerglings and zealots but not if you just leave them there shooting. Goliaths wreck carriers but only if you know when to target interceptors and when to target the carriers.
A good terran player will be able to defeat a protoss player making dragoons and zealots with only vultures in a properly microed rush. Dragoons are actually the counter unit to vultures, but with proper control vultures can still beat them with mines and just by simply avoiding them.
Also, it's not that difficult to max out your production early game. Decent players are pretty much getting the same amount of units at the same time, Koreans aren't pumping out double your units in early game. If you had a scenario where one terran player had 2 tanks and 5 vultures defending his base behind a wall and a protoss player had a shuttle, 1 reaver, 2 zealots, and 3 dragoons, the battle would be based purely on skill and control.
In something like AOE calvary will kill swordsmen no matter what you do, unless one of the players makes some huge mistake.