http://www.luxorcorp.com/
Anytime we get close to limits on the span, the engineers call for these engineered bridging, they call for glue and 10 nails into each joist.
I would guess that someone actually measured the difference between the different bridging. Solid blocking sounds impressive, but if you think about it, when the floor sags, the bottom of the joist is stretching, if it streches in both directions the bottom of the solid blocking would not stretch so gaps would have to be there.