I completely agree in most cases, however the Reuters article I linked was written earlier this week. Some market conditions necessitate a big swing in prices -- though guessing which direction prices will swing can be tricky.
If you wanted de-risk your position, you could set up an option straddle or just sell your shares before the announcement and then buy them again next week.
This is true in general obviously, but investing specifically is filled with explanations like this that make sense only in hindsight.