Wong's assumption that every winning bike since the 6.8kg minimum weight rule went into effect weighed 6.8kg is wrong. If he's going to make such a claim, he'd better provide actual evidence that is the case. There are articles every year listing actual weights of some of the bikes in the TdF, and those weights go up to 17+ lbs.
Except for Lance (who also insisted on getting the latest in carbon before his teammates) and a few other outliers, most pros are satisfied that their bikes meet a fairly lenient standard of stiffness and weight. But their main concern is reliability. The consumer market pushes the quest for more weight reduction.