The question made me consider other industries today:
Mortgage Servicing (the lenders who collect are mortgage payments): two players Wells Fargo and Bank of America collect between 25 and 50% of all mortgage payments!
Retail: How large is too large Walmart?
Banking: How substantive should deposits, credit cards, and other banking services be concentrated in the hands of Bank of America, JP Morgan, and Citicorp?
I undoubtedly am failing to identify similar concentration in many other industries. Your thoughts?