That's true in continuously quoted liquid markets like financials, but less likely to be true in real estate.
That said, I wouldn't touch FNM or JPM with the proverbial barge pole.
Home values no longer reflect the cost of labor,materials and local supply & demand. Rather they are instruments of speculation. The GSE are acting as banks without multiplier restrictions. How much money can the bond and MBS market funnel into real estate before they encounter or far exceed the systems natural limits?