Analysis of information sources in references of the Wikipedia article "Long March 2F" in English language version.
The principal difference between the Shenzhou-launching Long March 2F and its 2F/G cousin is easy to spot. The 2F/G carries a very different payload fairing at its top. This accounts. for the larger dimensions of the Tiangong laboratory, which wouldn't fit inside the standard payload fairing for the 2F.
It also lacks an emergency escape system. With no astronauts on board, the escape rocket and stabilizer panels that help Shenzhou spacecraft to separate from their rocket in a launch failure are not needed. This simplifies the design and also reduces the weight of the rocket. That's critical. Tiangong modules weigh more than Shenzhou spacecraft, so this helps to keep the overall launch mass within performance limits.
