that is because moss does not have tracheids and the only way water will reach the top off moss (it is quite short) is through capillary action. If moss grew in direct sunlight all it's water would evaporate and it'd die. Moss does photosynthesize but in shady areas where there is less sunlight. You know moss photosynthesizes also because moss does not grow in complete darkness.
**kanatana rolled a random image posted in comment #151 at Damnit Dad! ** I read your arguments; I especially liked the one comparing some posts to reruns. Genius.