When did it become a crime to succeed?

Lately the tech news sites have been filled with rumors about a possible antitrust prosecution against Google. Most of the rumors are based on statements made by Obama’s nominee for antitrust chief, Christine Varney. She has mentioned that Google has acquired a monopoly type of position in the Internet advertising industry and may be a future target of antitrust proceedings.
There is no question that Google has a very large and rather dominant position in the Internet advertising industry. The vast majority of Internet advertising is controlled by Google and that majority is increasing all the time.
But when people look at why it’s so large and why it’s increasing, no one cites dirty tricks or monopolistic practices as reasons. All of the analysts, even those critical of Google, point out that Google simply offers a better value than any of it’s competitors. It’s sheer size does give it the ability to offer more at lower prices, but that doesn’t change the fact that what Google offers is better than what any of it’s competitors offer. Google offers better value to the the customers who are buying the ads, as well the websites hosting the ads. A win for everyone.
So basically the reason Google is so successful is because it is providing a better product than it’s competitors are providing. And because customers have recognized this, Google has become the dominant player in the market.
So when did it become a crime for a company to be too successful? When did it become against the law to gain too much market share by simply being better than anyone else? Where is that invisible line between having a successful law abiding business, and a business that is now too successful and illegal?
Oh, and before anyone says this is a Democrat/liberal vs Republican/conservative thing, I would like to remind you that the Bush administration was making many of the same types of statements about Google. So this isn’t because the Obama administration is anti-business and the Bush administration was pro-business. This is a mindset that affects both parties.
Your business is allowed to be a success as long as it isn’t too big a success. Because if you are too big a success, then aside from any illegal or unfair dealings, your business could be prosecuted.