I do thing they just prey on parent's willingness to "do more" for their children, and the typical competition to make your kids look smarter and better than your neighbor's. In the process we all forget that children have less and less time to be just kids, to play and have fun, and we introduce them to the "rat race" at a very early age.
Steven Novella's Neurologica Blog has more on this: The Baby Einstein Hubbub:
It would seem there is no benefit to these alleged educational videos, and there is a suggestion of harm – although I would conclude that there is no long-term harm. It must also be pointed out that these studies are observational – not experimental. There are therefore many possible confounding factors. Perhaps parents who rely on these videos do so because they don’t have enough time to give to their young children – which itself is the factor that delays language.
He also blogged in the past on the newest fad: Your Baby Can Read – Not!, which I pointed to as well.
Remember, before your trust a TV commercial, do some research and go to the pros.