It really depends on how "invariably" she was late. If she was late almost all the time, and by 45 minutes or more each time, then it's patently irresponsible. She should have set a different time for the meeting every week. Or she should have blocked out her schedule to make the time. On the other hand, if she was late maybe 25% of the time, that's a different story. The CEO of a huge corporation is going to be late to a lot of meetings. It's the nature of the job. There isn't enough time in the working day for all the people, situations, and projects she needs to handle.

Having worked every now and then with C-level executives at huge companies, some much bigger than Yahoo, I can tell you that they're often late to meetings. Staff meetings especially, because staff meetings are standing, and standing meetings usually lose in an ad-hoc triage battle against spur-of-the-moment meetings. Almost axiomatically, anyone or anything important enough to hijack a CEO's time is going to be important enough to win the priority battle against a standing staff meeting.

All of that said, "invariably" needs to be defined here. Especially given the circumstances, i.e., requiring all direct reports in various timezones to be there every Monday on Mayer's clock. If it was, indeed, "invariable" -- as in, she was always at least 45 minutes late -- then she should have found a new time for the meeting. That's completely unacceptable.