All of the kits advise you to pre-treat or remove stains using the stain remover included. There is nothing particularly special about the stain remover in these kits.
Most stain removers are simply a cleaning agent in a water-based solution.
The water in the solution dissolves water-based stains, such as soup. Although the petroleum-based solvents work far better, both detergents and solvents aid in the removal of greasy stains. The informational brochure that accompanies home dry cleaning kits does not specify which of these agents is used in their pre-treatment solutions, and it turns out that the identity of the cleaning agent in the kits is proprietary information. However, given the kits' poor reputation for completely removing greasy stains like butter, it's probably safe to assume that they use detergents rather than oil-based solvents. The Dryel and FreshCare kits provide the stain removal solution in a bottle, along with absorbent pads that you use to sop up the dirt after you apply the solution.