they are not fungible, unlike houses.
Also, if you could copy a house like you could copy digital goods (i would download a car), i am also going to claim that the "monopoly" on the house must also be shortened.
You would download a house or a car, but the people making new houses or cars would only offer them for download if they can charge enough for each copy to make back their original investment. So houses and cars could be expected to cost about as much as a movie ticket or book or game. That those are currently much cheaper is also an indication that competition is successfully working to drive down prices close to the cost of production.