Why do we say 'bless you' or 'gesundheit' when people sneeze?

Many people have become accustomed to saying "bless you" or "gesundheit" when someone sneezes. No one says anything when someone coughs, blows their nose or burps, so why do sneezes get special treatment? What do those phrases actually mean, anyway?
Wishing someone well after they sneeze probably originated thousands of years ago. The Romans would say "Jupiter preserve you" or "Salve," which meant "good health to you," and the Greeks would wish each other "long life." The phrase "God bless you" is attributed to Pope Gregory the Great, who uttered it in the sixth century during a bubonic plague epidemic (sneezing is an obvious symptom of one form of the plague).
The exchangeable term "gesundheit" comes from Germany, and it literally means "health." The idea is that a sneeze typically precedes illness. It entered the English language in the early part of the 20th century, brought to the United States by German-speaking immigrants.
Virtually every country around the globe has its own way of wishing sneezers well. People in Arabic countries say, "Alhamdulillah," which means, "praise be to God." Hindus say, "Live!" or "Live well!" Some countries have special sneezing responses for children. In Russia, after children are given the traditional response, "bud zdorov" ("be healthy"), they are also told "rosti bolshoi" ("grow big"). When a child sneezes in China, he or she will hear "bai sui," which means, "may you live 100 years."
­ For the most part, the various sneeze responses originated from ancient superstitions. Some people believed that a sneeze causes the soul to escape the body through the nose. Saying "bless you" would stop the devil from claiming the person's freed soul. Others believed the opposite: that evil spirits use the sneeze as an opportunity to enter a person's body. There was also the misconception that the heart momentarily stops during a sneeze (it doesn't), and that saying "bless you" was a way of welcoming the person back to life.
We now know that sneezing is a reflex action and is most often the sign of something relatively benign, such as a cold or allergy. A sneeze also can be provoked by being outside in the sunlight or from smelling a strong odor. Still, we persist in the custom of saying "bless you" or "gesundheit," mainly out of habit and common courtesy.