Bike porn

I've never heard that one.
Shorter chainstays themselves make a difference according to bikeshop myth... er as tester says.

Well, according to Tester's very detailed response above (thank you), I can determine that short chainstays (aka mad toight clearances yo) should hereby remain the preserve of the Track Bike. Upon which, my theory holds true.
It stands to reason that a shorter driveline (in almost any prop or chain-driven device) increases acceleration response - ie it's more snappy.
You only have to take it to the other extreme (ie tandem/cargo bike) to see why.