One thing this seems to ignore -- a mortgage gives you _leverage_ for an investment. Is any bank going to loan you hundreds of thousands of dollars to invest in the S&P?
On the renting side, they only assume investing the money that isn't going to down payment/monthly mortgage payments, not investing the full value of the house.
My blog post here is just giving an argument that 2 of their parameters should be updated, then showing the result of that update.