Why Is Microsoft Telegraphing Its Strategy?

Something about Microsoft's latest warning to Yahoo doesn't make sense. The company said that if Yahoo didn't come to the table in three weeks, that it would go hostile in its bid. Why did it say what it planned to do after three weeks? Why didn't the company leave it more open, perhaps keeping open the door to a dropped or reduced bid?

Let's face it, the worst thing for Yahoo shareholders right now would be if Microsoft just walks. And this would be terrible for management, which would be facing shareholders totally out for blood. Saying they'll go hostile in three weeks isn't particularly intimidating. It might even be the easiest route for Yahoo management, because it takes the burden off of their shoulders.

So why telegraph this move like this? It seems to take the teeth out of the threat.