spillinmyRUM,
Yes, there are models with over-lapping sails. They aren't quite as simple to build, and I would imagine that's why there aren't more of them. There are 'who-knows-how-many' builders who reconfigure their boats to use them too. While it's just a guess, I would think that the "cost/skill" thingy is the reason for so few.
- 'Doc

PS - After just a quick glance, I think 'VMP' is tooling up for one like that.