Usually the investors, founders and board members fuck around with the corporate structure, option splits and preferred vs. Common stock so that the employee options are worthless, anyway.
That's not common in successful startups. No successful startup would want to alienate their employees this way. It wouldn't be worth it, just to recapture a few percent of stock.
Common stock only gets massively diluted when a company is in trouble. And usually startups in trouble end up dying, or getting bought in a fire sale, so in those cases the equity isn't worth much anyway.