Yeah, I don't quite get the point of trying to heat a home through water pipes embedded in a concrete slab on grade. Basically like trying to heat the earth at the same time. Not to mention the inevitable pipe breaks.
I once saw a show about a couple that lived in a Wright home. It was a beautiful place, with lots of nicely medium stained hardwood and panelling and built-in furnishings. But they said it required a certain lifestyle - the house forced you to live a certain way, in a sort of uncompromising way. Since Eichlers are designed by a Wright student, I would imagine they also have some uncompromising elements.
What's sort of interesting is that the Eichler home uses a post-and-beam construction. Whereas the platform version of balloon frame construction is far more common out here in the West. I've seen varied opinion on which is "better", more economical to build, better in a quake, etc. On the one hand the Eichler version of post and beam supposedly uses less wood. On the other hand the platform/balloon frame is supposed to be cheaper to build.