i recently received a adsense newsletter, it states: "Google is all about making money for Google. If you only select to have one ad group on your page, Google is more likely to populate that group with higher paying ads. If you have multiple ad groups on one page, Google will be forced to fill the many groups with some very low paying ads. Therefore, the average value of clicks on that page will be diluted by those lower quality ads. " is it true?