I don't have a problem with Doctors incorporating - but from the limited details in the article looks like there are multiple levels of corps dealing.  ie.  The office is one corp that employees the office staff and pays the rent and bills OHIP.  They then pay fees to the physicians who would be separate corps. This is my educated guess anyways. This setup would have both the physicians and the Office potentially using the Small business tax rate.  Instead of the corp using the SB rate and the physicians using the individual rate.

It is a similar structure to a company that uses self employed contractors instead of employees.  The difference being that most self employed people are not incorporated and therefore pay the personal income tax rates.