Day9 Question

Hey Sean,
I was just watching the BWC championships I got directed to, and in the semi finals (Sen vs PartinG), you were talking about the only 2 or 3 options Sen had vs the inevitable immortal/sentry push.

I was wondering about the validity of say a 5-8 roach + zlings attack at 44 supply? 2 base aggression...Obviously the pros could reach that faster than me, so in essence why would an early all in be < 1 cannon+1 stalker +(maybe 1+2 sentries)??
I'd imagine you could Just break the wall and rush 20 zerglings in. Proceed to use roaches as clean up and stream units to his door step... Is this just a past meta game that all pro's are constantly equipt to defend against, or has it been cut out by corners from the constant simplification of builds? 

I only bring it up because it seemed like a random play that Sen could have thrown at PartinG to at least try to vary things up in game 2. I feel like that level of play should be inherent, and present in competition, not just practiced calculations anticipated and reacted upon..

Well,I'm about to watch game 3, would Anyone like to discuss and explain?