Growing tomatoes upside down?

I have been curious about those upside down hanging pots for tomatoes that seem to be advertised everywhere.  At first glance it just doesn't make sense.  Plants need water, water goes down through the soil to the roots, it is called gravity.  Plants need sun, they seek it by growing up and moving to face the sun, that is called heliotropism.  I can't believe that watering them from the top doesn't lead to a bit of dirty water trickling onto the stems and leaves.  I have not tried these myself but after reading many forums and blogs I have come to the conclusion that they will grow tomatoes despite the fact that the infomercials make claims that defy the laws of physics. 

They are not for every situation, however. They lose moisture very quickly, and may have to be watered every day.  One must use plants that are at least 6 inches high when planted, use a type of tomato that will not grow too large and use very good soil, fertilizing every month. The claims that the pots last years is not born out by most evidence, they will need to be replaced, perhaps as often as every year, because the plastic does degrade fairly quickly. 

The bottom line is that they save space and the tomatoes ripen a bit sooner, but the plants are not as prolific as they would be growing them the ground.