Nobody really gave much thought as to why Google's growth in paid clicks was stagnating, the common assumption being that the economy was in a funk, and Google had no more room to grow at present. Appears that there are other, and valid, reasons.

Such as the fact that Google intentionally reduced the number of clicks by increasing the cost per click for some keywords. Which left their revenue growth intact while leaving a superficial impression that clicks on Google's ads were suffering. Which is what led to the surprise bedlam when the first quarter results came in.