That beautiful image of a cresting wave that you've seen on banners and promo shots of OS X 10.9 Mavericks is meant to represent the surfing spot that the OS is named after. As with all OS X operating systems, Apple usually spotlights one wallpaper as the default desktop image for marketing material. This image is always included as a new wallpaper in the OS when it ships.
However, if you don't want to wait for OS X 10.9 Mavericks in the fall, you can download the wallpaper directly from Apple now. What's interesting about this wallpaper is that it comes in 5,120 x 2,880 resolution, which is higher than the resolution of any Mac currently on the market. Is this a sign of Retina display iMacs to come? Could be.