DC in the house doesn't remove the need for switching regulators - you still need to step down from the house voltage to the device voltage. Don't forget that devices that accept 5V or 12V from a wall wart almost all still have switching regulators to step down to 3.3, 1.8 or less. It does remove the need for transformers and rectifiers, which would buy us some efficiency.
And don't forget that if the house DC supply was at less than 120V, then you'll loose more power in the house wires, because the electrician who wired your house was too cheap to buy superconducting romex.
If your house is wired with the lights and the outlets on separate circuits (mine is, because I'm an EE and I built the house), you could change out all those lights to low-voltage LEDs and supply 12-24VDC to them and light up your house just fine on the 14-gauge copper romex that's in your walls now. This works because the required current would still be well below the 15A at which the wire is rated. (Getting your electrical inspector to approve it might be another matter, though.)
In some cases, this trick would work for the outlet circuits too because most of the things we plug into outlets now are low-voltage DC wall warts, and they could be replaced with low-voltage DC-DC converters. The problem is that your refrigerator and your dryer are not run by wall warts, so outlets are tougher to convert to DC than lights.
True, I should've written "rectifiers and filters." The inductor(s) are most likely still going to be needed, but you can get rid of the diode and filter capacitor losses on the primary side.
And don't forget that if the house DC supply was at less than 120V, then you'll loose more power in the house wires, because the electrician who wired your house was too cheap to buy superconducting romex.