Why invest in tracking the DOW Jones index when it is price weighted instead of market cap weighted like the S&P 500? what's the difference?

10 year comparison:

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In a market-weighted index, if a company representing 10% of the index goes up by 50% (say), then the index would roughly go up by 5% if other shares flat. For a price-weighted index, it depends on the dollar price of the different shares and cannot say for sure what would happen to the index.

For this reason, market-weighted indices are a better representation of the overall performance of the market and much more common to find instruments to track.