If I were to guess, I would say a lot of it can be attributed to 2 actions.

1 The way the PPT operates to manipulate the markets: They buy options against indexes. This causes all the stocks in the indexes to move in concert due to market maker computer driven risk management.

2 the movement of $s into and out of the markets: when large houses and funds wish to raise or reduce $s (for any insane reason) all the stocks in their portfolio are subject to the same buy or sell pressure.

I believe that we have seen a number of days where the trend is broken and that in the future this trend will be smashed when investors turn to the metals for their safety in light of rapidly deteriorating fiat.