Google claims it is now the consumers turn to customize, just like how Bing has a similar feature, with was also borrowed from Ask.com which offers themes.
I know I always liked seeing new Google Fonts, and designs on certain days, whether it was someones birthday or a national holiday, that Google had customized. I know I will want to use Google even more to see new pictures constantly changing. They are attracting the users, and it is constantly competing with other search engines, while at the same time advertising through an interactive way. Im sure Google does not need to be worried about loosing users, but if they were this is a sure way to pick up more people, and keep their page fresh.