Your anology is wrong.
The processor would be the engine, the gas tank would be the battery.
Consider the 1 Ghz+ (and now dual core) processors with embedded gfx cores as hungry, loud, powerful high revving v8s.
Now there are accepted sizes for phones. People just wont buy a 2 pound 5 inch x 6 inch monster. There is only so much they can cram into a small space while still maintaining the perception of a phone. Also price is an issue, and like someone pointed out, there is already an extended battery for it.
Would you really want to pay more than 600 dollars for a phone from the manufacturer? Learn to use it less, get another battery, or stop blaming them.
Sent from the Blue Falcon cockpit on my Fission 2.4.3 D2G