In Level D it should and does!
Three components to the "automatic" flight contol on the 767 (757 also):
1. Autopilot
2. Flight Director (cross hairs on the artificial horizon or EADI)
3. Autothrottle (or autothrust)
There are TWO ways of flying automatically:
1. Through the MCP or Mode Control Panel by selecting speeds headings altitudes or vertical speeds.
2. Through the FMC which itself will decide the speeds headings e.t.c. based on your input data.
The autopilot has various modes of contol: Altitude, Heading, Vertical Speed. LNAV and VNAV are auotpilot modes which effectively couple the auotpilot with the FMC.
The autothrottle is not part autopilot system. As such it has a separate switch and can be used independently. So, in theory you could be hand-flying the aircraft by climbing and turning but with the autothrottle maintaining your selected speed - and remember that you must select a speed in the speed window for it to maintain. The engines will power up or down to try to acheive the speed.
That why, as pointed out, pilots can choose to disengage the autopilot but leave the autothrottle engaged whilst flying.
Another classic example is during takeoff. You "arm" the autothrottle by switching it on. Select a speed that you want to climb out at in the speed window. And when cleared for takeoff you press the N1 button and the throttles move up automatically. Once airborne they'll maintain your chosen speed by guiding you with the flight directors, if you've pitched up too much you might lose a bit of speed so they'll commnd a pitch down. All this whilst you're flying it by hand!
Hope this helps.