Yes they are!
However, those things have to be replaced when they run out of ink, go out of style or the pages get worn (or in the case of the KINDLE; the battery dies)
Simple things cost us nothing. Like a smile, or a walk in the park or just around your neighborhood.
How many of us take a walk in our neighborhood just to see things that we pass every day on our way into our own small universe called, "home".