I agree with Rand. It's the duty of the CEO and other executives at any company to maximize return on investment for their shareholders. If Apple executives were to voluntarily increase their tax payments - thereby decreasing profits - they would not be properly executing their office and duties. This is especially true when their competitors choose to maintain the legal advantage.
The entire hearing is a farce and should have been reversed: citizens of the US grilling legislators about why they implemented tax laws so poorly that exploitation of loopholes is common practice. I think many of us have suspicions as to why this is the case.