Absolutely, but the cost is too high. You need to gasp gather people in a room, give them your product and somehow record their reactions. Don't forget that it takes real work to pick out focus groups since the dozen individuals you do use are supposed to represent your entire market. On the other hand, Google is dealing with hundreds of thousands to many millions eyeballs at once. And they have a definite metric: did the person click on the ad? Yes, using the wrong color blue is going to cost them a thousand clicks during the trial, but now they have the perfect color for the next year or two.