The OP provides a good technical explanation. Unfortunately he fails to mention another closely related term to high frequency which is what makes this type of trading highly lucrative: 'Front running'. See http://en.wikipedia.org/wiki/Front_running .

Front running is illegal, but if you look for successful cases of high frequency trading they are generally tied-to/accused-of front running. And as you might imagine, in order to do front running you need to be high-up on the food chain (i.e. be a market maker)

The missing key about front running in the article is the 'anonymous' bid-ask: "The matching engine takes his order and displays it (anonymized) to all other traders with a data feed." and "She places her orders, and it is again displayed to the world (anonymously) and stored.".

If you have forehand knowledge of the bid-ask (i.e. non-anonymous) the market maker can front-run and with high-frequency make a considerable profit.