04' Hybrid Gas Milage

First off, when you buy a civic hybrid you look at the gas milage and see the fuel consumption by the govt. states 35 city and 49 highway, but while traveling from Phoenix to Los Angeles I averaged only about 30 miles per gallon on the highway, this baffles me because i have an 05' CR-V that gets 28mpg on the highway and has more room, any suggestions or experiences with this same or similar problem?