Perhaps a simpler way to answer this is the private insurers pay a fee to the government for the risk that's inherent to the government for the 90% guarantee. To the extent that private insurers earn market share--and they do, they have about 30% of the market--I think the key difference is all the income from CMHC is the Government of Canada's, whereas in the case of the private sector insurers it's the fee relative to the risk that's assumed, and the balance of the profit remains with the private shareholders.
On June 20th, 2011. See this statement in context.