the writer is i guess still a student.. he has not considered the residual value of the investment.. in loan method your value of house at the end of 20 yr would atleast be double (pessimistic view) accoringly, net you would have spend 2.4 million (7.4 - 5).. whereas in rented you would spend 4.6 million to stay in a house for 20 years.. this itself shows that the analysis is incomplete.. and remember i am still not talking abt validity of the calculations !!!
