If your home was built with carpeted stairs it is likely that the staircase below the carpeting is cheap, construction grade pine. Many homeowners prefer the look of hardwood staircases. With a little retrofitting it is possible to add real hardwood stairs on top of your existing pine ones. The photos below are from a recent job where I did this.
Phase One: Removing old stair threads.
Phase Two: cutting the nose off the old threads.
Phase Three: Fitting in first new step.
Final Phase: New stairs installed.