The post you have been discussing:
http://infoproc.blogspot.com/2008/10/regression-to-mean.htmlis only a pedagogical example and not meant to be realistic. Its purpose is to illustrate that if there is a non-genetic contribution to intelligence, which is not perfectly correlated between parent and child, then regression must follow even if the genetic component is perfectly transmitted. Taking G and E to have similar effect on IQ, and similar standard deviations, was only to make the mathematics easier. Even if GxE effects are significant, or parental E is somewhat correlated with offspring E, one still expects regression from a similar line of reasoning.
You can find more detailed analysis here:
http://duende.uoregon.edu/~hsu/blogfiles/midparent_offspring.pdf
Regarding environmental effects on IQ, you may want to read up on shared vs nonshared environmental effects in the behavior genetics literature:
http://infoproc.blogspot.com/2009/11/mystery-of-nonshared-environment.html