I think the real key to why GOOGL is thinking this way is so that they can capture some purchase history. Search gives GOOGL a unique insight into a consumer's purchase intent. However, that can lead to wasted ad serves (I comparison shop for a computer on line...my intent is to buy a new machine. If I make the purchase away (say at a best buy or on AMZN), GOOGL has no way to know that the purchase was made. So, each computer ad I see for the next month is a wasted impression...if GOOGL can gain some insight into what I've purchased, they can target better ads later (in this example, serves for a new printer, or more screens, a better keyboard, etc).