The Chevy Volt is like this -- drivetrain is electric, gas engine is just a generator.

What you are describing is a “series hybrid”. The Chevy Volt is not a pure series hybrid, it has an elaborate mechanism to connect the gas engine to the wheels when it is efficient to do so. For example highway cruise where the gas engine can run near its optimal rpm.

This is how hybrids work at low speeds. They use 2 motor/generators - 1 to push the wheels, and the other to refill the batteries.

Most hybrids use a slightly different engine, which is more efficient but generates less force. The hybrid transmission can add torque when accelerating or going uphill.

The engine must get less wear. My Camry Hybrid only needs an oil change every edit: 10,000 miles.

   My Camry Hybrid only needs an oil change every 5000 miles. 

That's not an impressively long oil change routine - pretty typical for a newer car, was that the correct number?

No, but you don't need a complex drive train, like modern plug-in hybrids have.