Fast rushes aren't pointless. It's about scouting. Even if you're expecting it, you have to be careful not to fall to it. Even if they're not able to wipe you out, it often causes players to go into turtle mode, which can mean a huge advantage later in the game.
And I find it unusual that the games you watched were all air/mass army.
First off, Protoss have very expensive air, so they rarely go air. Second, most games are decided long before the 200 unit limit is reached.
You can always just play Protoss or Terran and wall yourself in. (Zerg typically doesn't need to)
Then you can turtle to your hearts content, but you'll usually pay dearly later because your opponent will be controlling the whole map.
Note when I say rushes, I don't mean LOL ZERGLING RUSH. I mean getting quick tech, scouting, and such.
Also, rushing actually takes a supreme amount of skill. The build orders aren't the hard part. It's the management. If you just send your units in with attack-move, as long as your opponent is even remotely familiar with the game they will not fall to it. What makes it dangerous is when you can keep them alive and only take out the most valuable targets. It's rare that someone loses immediately to that, but it hurts them over the long term.