To be fair, Apple (and I'm sure Google) does this too. There is no doubt in my mind that Apple is going to announce a milestone of it's own tomorrow[0], a day that just happens to be the day of the Google I/O keynote.
Apple has done this before announcements (software updates usually) but not regarding iTunes app sales milestones. I'm of the mind that it is a coincidence.
Google's done the same as well after Apple events such as them announcing they would drop h.264 for Chrome which never came to fruition.
Google's done the same as well after Apple events such as them announcing they would drop h.264 for Chrome which never came to fruition.