Most of the lift comes from the main wing, and in fact the tail lifts down, so the main wing also has to support that.
(That's for a stability reason.)
The lift of a wing is roughly proportional to two things:
- angle of attack, and
- airspeed squared
so, the slower an airplane is flying, the more it raises the nose.
You will notice this the next time you fly.
At cruising speed, the plane is at around 300 knots (a knot is about 1.16 mile per hour), and it is pretty flat, with an angle of attack in the range of 1-2 degrees.
(At altitude, 300 knots corresponds to a much higher ground speed, due to the thinner atmosphere, but that doesn't change the lift relationship.)
When the plane is maneuvering in the approach pattern, its airspeed is more like 150 knots, half of cruise speed.
So it has to have roughly 4 times as much angle of attack, anywhere up to about 8 degrees, thus the high nose.
The maximum angle of attack is around 19 degrees, at which the wing stops working.
The crew has to stay well below that in order to have reserve lift in case they need to pull up suddenly, like if they hit a downdraft or wind shear, or if they have to turn quickly.
That beautiful photograph of the 747 was taken by another plane flying in formation with it, and for a photo shoot it was probably not travelling at cruising speed.
(It's also not very high, unless that's the Himalayas in the background.)
Best Answer
The airfoil shape is optimized for two features
Maximizing the lift coefficient $c_L$ alone would, as you said, demand for a semi-circle-like shape, like this:
Minimizing the drag coefficient $c_D$ alone would demand for a tear-drop-like shape (with a round front end and a thin back end. See the streamlined body in the image below.
(image from Wikipedia - Drag coefficient)
Putting these two requirements together you arrive at the typical airfoil shape which is kind of a compromise between the semi-circle and the tear-drop shapes from above.
(image from Wikipedia - Airfoil)