Never seen a factory application use them. However if a vehicle was being shipped to a year around warm climate the need is reduced as the use of the center heat riser passage is to quickly warm up the carb area which helps fuel atomization at cold start up and also helps eliminate throttle blade icing during the winter months. In the summer months the heat riser really isn`t needed. Hot Rodders believe in keeping the intake cool as possible which is why many use the restrictors or block off the heat riser passage entirely.
I`ve seen gasket sets come with the restrictors, but never installed. However since yours came that way the only answer I have is they are acting as the restrictors for the EGR valve but I could be wrong so don`t quote me on that.