Vulgar Marxism is an analysis of industrial capitalism--it is an 18th-19th century mode of production. Technological development is industrialization in its concrete form. It is a mechanical innovation and forever transformed labor. Originally labor came through humans and animals--such as workers operating the textile industry or horse drawn ploughs. Basically these sources of labor used the body and muscle power. Yet through technological development labor is liberated and the efficiency of labor is thus increased. Yet mechanical labor is not free, it costs money and the cost is generally coming from someone else. In a way, we are literally living off the backs of dead animals and their stored labor. In other words, the heat used to warm our homes comes from fossil fuel, which is technically composed from the remains of dead dinosaurs and other once living creatures.
As mechanical labor began to gradually replace human labor, thus people became less central to the production process.
Additonally, in class we learned about use value and exchange value. Use value is what something is worth to you. Exchange value on the other hand is the idea that everything has a value and the result is that it determines how much you can sell something for, such as one's house.
Here is a link further discussing exchange value