I don't see where you're giving credit for principal reduction or the effect of the tax benefit for the principal payments.
But regardless I would say don't buy a house unless you have 20% to put down, because PMI is a killer. I am also (now, after several mistakes) a firm believer in the 15 year mortgage
My history of owning houses is as follows:
First house-terrible decision-bought a year out of school, thought we HAD to own a house. Wrong neighborhood, no down payment-wound up selling for $7000 loss after 7 years
Second house-fixer upper great neighborhood in the suburbs. Even though we owned it through the bubble burst we sold it for twice what we paid after 17 years.
Third and current house-retirement home in townhome development (I would only buy an end unit with a 3 car garage as the market is not flooded with those). After 8 years we have about $120K equity and will have it paid off in 10 years (I hadn't become a believer in the 15 year mortgage until we bought it.
So end of the story, real estate can be a good investment if you do it right. Don't trust your realtor because they get paid either way. Find someone you trust and run all decisions by them.
"...and the loan would be paid down to $125,000." Tax benefits are minimal, so throw them out. I was trying to respond to the previous poster's worry that a house would hurt their net worth, I beleive he was including the total of all payments (principle and interest) on the liability side of the ledger and not just the principle left to pay.