LOL! Economy is for tree hugging hippie fartknockers. The trade off is always power versus economy - with technology and increases in efficiency, over time more power is achievable with the same amount of gas (see: fuel injection, direct injection, variable valve and cam timing, cylinder deactivation, etc.). To answer the original question, the people demand power, so manufacturers provide it, or they go out of business.

As an aside, I find it hilarious that the idiots whining about fuel efficiency are also the clowns demanding more safety features of dubious effectiveness, which all have a non zero weight.

Anyway, I remember thinking ye olde Volkswagene with a whopping 100hp was the bomb. Now I can't live without at least 250hp.