Is there evidence that this explanation is more true now than in the past? It's probably worth at least examining whether they have become more capable of acting out that preference.
This means that the labor (ordinary workers) gets less leverage and capital (owners/managers) get more leverage, i.e., increased ability to ensure that they get a larger share of the pie.
The ancient dictator needed his slaves to work to build his pyramids. The feudal lord needed his serfs to work his fields. They needed to ensure that they are kept from rebelling but also can live well enough so that their numbers (and thus the lords' power) increase.
The industrial capitalist needs to keep the working class somewhat satisfied (bread and circuses?) - they are absolutely vital to his needs, and if they self-organize and start striking, he loses.
However, in the far future when everything is automated, whoever controls the means of production doesn't need the underclass in any way whatsoever. They may care about their community, but letting the underclass to starve or machinegunning them isn't an impossible "solution" anymore. Neither the slaver, nor the feudal lord, nor the industrialist could afford to eliminate everyone who's discontent, even if they physically could do so after crushing a rebellion - they needed their labor. In the future, that won't be the case; the only thing preventing a ruling regime having their robot army slaughter the unneccessariat is if they choose not to do so and choose to share the wealth instead.
I believe it may be related to a broader cultural shift towards individualism (see, e.g. http://www.hup.harvard.edu/catalog.php?isbn=9780674064362)