Vestron's Law: What is it?

Vestron’s Law states that:

when publishers or content producers in non-print media license rights to third-parties, over time the pressure builds to revert those rights. McGraw-Hill thus joins other book publishers, journals publishers, Hollywood movie studios, television producers, and newspapers in viewing subsidiary rights licenses as short-term opportunities and long-term obstacles for developing their businesses.

[ From "Vestron’s Law: The Propensity for Rights to Revert to the Original Publisher" from the Society for Scholarly Publishing's blog the scholarly kitchen ]