In this context, I guess the self-employed would be an intermediate 'middle class'. A doctor or accountant with her own practice, a master tradesman who can pick and choose his clients, a programmer who does contract work for companies - none of them are propertied enough to have their own workers, but neither are they employed by a boss who takes a cut of their pay. But I agree that a lot of people who call themselves middle class are actually either upper class or working class.