I imagine the index creating company would have many experts analyzing the market and sell the index information.
Do they sell this information to multiple brokerage companies? If yes, then would there be much difference if I had invested in funds from either of these brokerage companies which target the same index?
The companies which define the major indexes do not derive profit directly from the indexes. They are typically brokerages, which use the indexes as a tool for discussing investment options with their clients and as a publicity tool to remind the public that they are long-standing, respected firms whom we might want to consider working with. Can't mention the Dow without being reminded of Dow Jones, for example. Likewise the Standard & Poor's 500 reminds us that S&P is still going strong.
There may also be some slight market manipulation opportunities in choosing which specific stocks are included in each index, but since investors rarely follow an index exactly as originally defined I'm not convinced that's significant. And the mix included in each index changes relatively rarely and has to be justified by what the index claims to be representing.
