Why is Nasa replacing the Shuttle for a 1960s replica?

The Shuttle was designed to lift payloads into space and conduct "near earth exploration". Orion was designed for a manned mission to mars so they are going with a design, while much larger that the original, is similar to the moon missions. Where a trip to the moon took 2 days, NASA has figured it will take 2 years to reach Mars. This means a tremendious amount of materials need to be lifted into space(food, fuel, supplies for 2 years). The way NASA figures is that they will send the living quarters and most supplies out first and have the crew and landing vehicle go last. The reason they aren't going with a winged design is that the speed nessesary to get to Mars would rip the wings off the craft on reentry. Where as a capsule can use the atmoshpere better to slow itself down.