Plagiarizing a link from a similar thread above, here's a discussion of the issue:
http://www.import-car.com/ic/ic40024.htm
AFAIK, it's not that the single-row chain breaks, but that it stretches a bit sooner than the double-row. It's chain stretch that allows the chain to slap against the plastic guide rail, which when it's old and brittle breaks, which leaves a piece to get caught in the chain and cause it to jump a sprocket, which causes mistiming and valve damage in the engine that Jack built.