No. All factors devolve to labor. Why does a neurosurgeon earns more than a welder? It takes a decade of labor in college, as an intern, and on the job to become a neurosurgeon. It takes about 2 years of labor to learn welding. Risk also increases the value of labor. A neurosurgeon typically pays about $200,000 per year for malpractice insurance, and the value of his labor is adjusted to offset that cost. Why does a Rolls Royce cost more than a Kia? Why does a meal at a Michelin Star restaurant cost more than McDonald's? Skill requires labor, the higher the skill level, the more labor is required to obtain it. The more skill it takes to provide a product or service, the more expensive they will be. The more labor it requires to obtain a resource (like iron, wood, gold, fish, or truffles) the more that resource will cost. Marx certainly believed that value was derived from labor, the "Labor Theory of Value" comes from Adam Smith, that a commodity's value was based upon the time and labor required to produce it. Marx fully agreed with this theory, the only thing he objected to was the division of that value.