By buying $1mil of MSFT you helped set the market price for their stock and therefore value the company. Based on that value Microsoft can then go to the market and raise new capital.
That is presuming that MSFT ever issues more stock. They haven't appreciably done so in the past 15 years, and the same trend applies for most of the DOW.
If MSFT never issues more stock, what then? Furthermore, helping to determine the value for possible future issuance seems like a very marginal benefit relative to the overall volume of stock trading.
