Very interesting comments from all. (If I understood specialitely GTR LVR's comment right) I agree with this one, do not understand the lower prices of the GTR's. GTR is one of the rarest things what could have. But maybe this has something to do with the GTR's roughnes if it can be say like this.
The road car is much more comfortable (I think) and it has quite many luxury things added which are missing from GTR's. So a person who want's a GTR, knows precisely what he wants and probaly is very specialised about GTR's. The markets are lower, the demand is lower.
When someone, who wants a perfect road car and have not problems to pay for it and wants to use everyday everywhere, and comes even cheaper to own, and even can take two friends onboard; chooses the standard F1 roadcar. And this could be the reason, that in the end; the roadcar versions are more expensive....
Am I totally wrong road now...?