They were following the "she's on a break until Easter" plan until they released the Mother's Day photo, an epic fumble. (It never should have gone out as it did. Bad PR staff work.)
I must admit that I laughed out loud at the idea of the media looking "incompetent." That's a story that will NEVER be reported!
Ultimately, the media is like a hungry animal that needs to be fed constantly. This week, it is feeding on the fact of Kate's announcement. Soon, it will be hungry again. Unless Kensington Palace feeds it something, it will grow its own messages to fill the void.
As I said a few days ago, Buckingham Palace has been handling that "feeding" very successfully with strategic photo ops, videos, and comments. Unless KP does the same, we'll be back to conspiracy theories trying to fill in the blanks. (And, I'm not endorsing that scenario as something that I would like to see happen, I'm just stating what I believe is likely to happen.)