In Europe, in the middle-ages... "guitars" were shaped like that... It wasn't really until the English countries shared lutherie techniques with the Spanish countries that you have the acoustic guitars that you know today. Which were based off the style of classical guitars that the Spanish built.

Ovation makes their guitars like that becasue they say they resonate better... I have an Ovation 12 string and I personally am not very fond of the sound that it emits... I don't like the composite back...