How do the E commands in G-code work, exactly?
Yes, the absense of an EX.XXX (or an EX.XXX with the same value as the previous one) means nothing will be extruded during the move. The extruder is treated as an imaginary fourth axis and works exactly the same as any other axis: if in a G1/G0 no new coordinate for it is specified, it retains its original position.