Considering different studies have produced different values of heritability, I'd have to say that to so confidently dismiss the significance of social variables is out of place.
"Intelligence: Knowns and Unknowns"
Gives heritability a value of 0.45 for children and 0.75 under and after adolence".
A newer study ("Genetic influence on human psychological traits - A survey") gives 0.85 for adults.
If we assume that heritability is logistically distributed over age it would be quite easy to calculate a value which could make some sense independent of age.
The point being it would always be under 1.00, it would be of course in the greater half line of [0,1] which reflects that IQ is to a somewhat great extent hereditary.
However, heritability is not independent of the social variables and vice versa (socioeconomic standing of your family etc.), so even with a high heritability value it says little of to which extent social variables effect the performance on IQ tests.
Summary:
Heritability factor is significant.
This does not immediately imply that social factors are insignificant.
(They are not mutually exclusive.)