Quote from ammo: ibm 1 of 30 stocks, ibm 1 of 500 stocks,i don't know the weighting anymore but spx and dow are weighted differently considering dow is all blue chips
I agree with your reasoning, but DOW and SPX always move more or less in tandem everyday. This has been the case going back as far as I started trading. Check the two charts.
Naz, of course, doesn't follow this logic. It moves on it's own terms and conditions.