Before you can discuss business, you've got to understand the vocabulary. "Advertising" isn't a synonym for "marketing."
Like other large marketers such as Procter & Gamble, Kraft Foods, or Unilever, Microsoft spends huge amounts on marketing (including advertising) to create demand for its products.
Still, this thread isn't about marketing or advertising; it's about the Bing search engine's market share. Can Microsoft use marketing (including, but not limited to, advertising) to achieve what it hasn't been able to achieve through bundling or consumer demand? If Comscore's numbers are accurate, how much has it cost Bing to achieve its larger (but still small) share of the U.S. search market, and can it sustain that growth rate while achieving and maintaining profitability? Can Bing become a serious competitor to Google if it doesn't find acceptance outside a country that has only a small percentage of the world's population? You can dismiss Google as a "marketing company" if you wish, but right now, Bing is a small player in a limited market, and it's a pretty safe guess that most of Bing's gains have been bought with marketing (including advertising) dollars.