From the few company announcements I listen to, it seems common for the CEO of the company to be emphasize the good, and de-emphasize (or omit) the bad. Anything less than great confidence is perceived as weakness, and the last thing a CEO wants to do is imply to shareholders that they don't know what they're doing.
Of course, I don't believe her words excuses her poor performance. Rather, it's important to recognize that her words are rhetoric: not necessarily things she believes but things she must say in light of the various pressures acting on Yahoo.