1.
Diagram A: Resistor R4 limits output current. (Similar to limitations as found in a typical class A amplifier.)
Diagram B substutes the transistor Q7 for a resistor. The transistor can be turned on to allow greater current flow at the output, and produce wider swings of output voltage.
2.
In Diagram A, the bias leg is automatically more than .6 V above the emitter leg. This is the non-inverting input.
Same with Diagram B.
The addition of the resistor divider makes it easy to shift the output's DC component up and down (within limits).
My knowledge is incomplete so this post may need some correcting.