The 150-fold figure might apply if they actually took divergent paths back to Earth by a degree or two, but that doesn't seem to be the case--they took very nearly parallel tracks, with a few meteres of random jostling one way or the other. I'm not sure how much effect the explosive detachment from the shuttle+main tank has though / which way those forces are directed.

Interesting reading here on the details of the booster rockets: http://science.ksc.nasa.gov/shuttle/technology/sts-newsref/s...