Thought I'd just toss in some amplification. Tech wasn't decreasing flow, he was increasing velocity. You increase velocity by cutting down the cross-sectional area of the manifold runners.

Fluid flow, excluding compressibility:

V = Q/a, where,

V = fluid velocity
Q = fluid volume
a = cross-sectional area of the passageway.

Q will try to remain constant at a given RPM, since the engine is simply a big heat-producing air pump. Therefore, if a (the area) decreases, the V (velocity) increases.

This is a very simplistic approach, but it illustrates Tech's premise.