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.