This idea comes from a business colleague, Gregg Vojik, who has done his share of houses too (including those in other states). He achieved this rounded corner on all of his walls by adding small cove molding instead of corner beads and then applying the drywall mud over it. Look too at how the bottom was done to blend into the floorboard.
While Gregg didn't have an estimate for how much more this would cost over standard corners, the only extra cost is really for the cove molding as the labor is pretty comparable. This really provides a nice soft look to the walls.