Well my take is this, The better quality of the component parts means less tweaking. That doesn't always mean the most expensive, and hardly ever means the lightest, but a good, well built dérailleur is going to stay in adjustment better than a poor one. You can go the "Dutch" route, and buy a Bakfiets, but riding that on a 20 mile commute might be a bit tiring.

Secondly, power losses on a car are hard to notice, and have only an indirect impact, "Why is my fuel consumption so high these days?" On a bike, your legs tell you about every watt you expend, you feel every "grind, grind" every poor shift, and so on.