Not disputing the hard work, but at key points in Microsoft's history, they've held and exercised tremendous monopoly power, generating large margin at the expense of their customers.. Just like Slim's companies in some respects.
A clearer example is Google: it has an effective monopoly on search, but it's not because it has lobbied Washington to stop people from using other search results, it's because it was the best search engine, spread like wildfire, and kept the market ever since. People use Google not because there's no other (legal) search provider available, but because it's still the best way to find things on the internet.
Because of this instinctive understanding of the value created, it's much rarer to see Brin and Page criticized for their wealth.