Do not think that the participation of Schmidt in the Senate antitrust subcommittee has willingly. The interview, scheduled for September, only happens after the senators made it clear that unless we agreed to go for good, former CEO of Google could be forced to go foul.
The senators want to know Google? Basically, as the company deals with its competitors and what are the practices that Google takes to ensure its dominance on the Internet. The committee notes particularly antitrust and corporate business practices of the companies investigated.
This is not the first investigation an eye on Google. Last month, the Federal Trade Commission (FTC) also announced it would investigate the attitudes of the seeker. Until now Google says it has nothing to investigate and explain what, but agreed to provide the documents that the FTC order.
There back in 1990, Microsoft has complicated investigation by that same nature. They spent millions of dollars in their defense, in addition to closing agreements and change products to meet requirements of U.S. authorities. It seems to me that Google is going the same (and torturous) path.