For London-based bookmaker William Hill PLC, getting licensed for betting in Nevada was not optional.Rather, it was essential to moving forward with online gaming ventures outside Europe, according to Ralph Topping, chief executive officer of Hill PLC, Britain's biggest bookmaker.After all, the Silver State is the gold standard of government regulation and promises an unrivaled rich vein of cachet in the event of an online gaming rush.Having won approval from Nevada - for decades, the only place to gamble legally in America - Hill aims to buy companies or form partnerships in South America and elsewhere in North America, he …