2008 GMC Yukon Two-Mode Hybrid
One thing that's been repeatedly noticed over the last few decades is that as new technology is added that improves cars and trucks, drivers have a habit of adapting in a way that negates that benefit. When ABS started to become prevalent in the early nineties drivers compensated by driving more aggressively, particularly on poor roads. As a result NHTSA and insurance industry studies indicated that multi-vehicle accidents were reduced because drivers were able to avoid obstacles by steering while braking. On the other hand, single vehicle accidents increased as drivers discovered that ABS can only allow you to approach closer to the limits of physics but not beyond.
Similarly as CAFE standards have been stagnant for going on two decades now, the fuel economy of the vehicle fleet has also remained stagnant. At the same time power output has risen pretty dramatically meaning that specific fuel consumption rates have also improved. If the balance between power and consumption had been steered toward efficiency, we would already have much higher fleet averages today. The problem comes down to customer demand and fuel costs. Fuel costs have remained at historically low levels when inflation is factored in. As a result on the vast majority of vehicles, when offered a choice of power levels, the bulk of customers go for the higher outputs.
The same appears to be happening with hybrids today as the average weight of new hybrids has climbed thirty percent between 2000 and 2006. Drivers have started migrating toward ever larger vehicles with hybrid powertrains thereby negating the benefits of a hybrid. Of course looked at another way, the hybrid should at least be a little more efficient than a vehicle with similar net output. Or not, depending on your driving habits.