Thanks a lot va_landload! your answer is inline with

what I thought, that is, the cashflow is calculated not only by initial downpayment of a purchase, but also need to be factored in the opportunity-cost (the equity can earn interest as well).

btw, I recently saw a reo house for sale, and I called only one day after the info was make public, the listing agent called me back in 4 hours and told me the house was under contract! Tough mkt for reo investment...

good luck on your next bid :)