Michelangelo painted ceillings and its art of its finest. It doesnt make a difference wether you paint walls, floors, paper or digitally on a computer, its all the same and none is less art. Art covers wide variety of catagories, sculptures for example are one, did you ever question them as art too? Some people even call a crumpled piece of paper art, so actually there is no general definition of art, one has to decide for themself what they consider art. The saying:"Beauty lies in the eyes of the beholder." could also be used in this situation.