portland,
The theory is that it gets them in the house. Less than half a percent of Americans get a 30 or 40 year mortgage and keep it for the duration of the terms. They do one of two things....refinance or sell.
LVR, Great product!! I have an interest only on my house and do the same thing. Why let the bank earn the interest when it frees up monthly cash flow for the borrower...oh and the best part for agents....it allows the borrower to buy more house.