Facebook's core advantage is the social graph, not the infrastructure operation, which is Google's thing. Consequently, Facebook has tight grip on the access of its graph whereas Google keeps the secrets about its search algorithm and server setup. By open-source it, Facebook is not only getting good PR but also undercutting the competitor.
Google has technical ability to stay on top of spammers, but may not have enough incentives in the short term for ads revenue or lack of competition. Also, their foray into mobile platforms, social networks, and TVs etc comes with huge opportunity cost - at the end of day, the top guys can only have limited attention.
Apple never introduced products "You'll never forget" without a media event. Apple would describe their products as "magical", "amazing", or "revolutionary", but "Tomorrow is another day", "You'll never forget" is personal. It has an obvious sense of lyrics. And music, include that from the Beatles, is to most people unforgettable. People has an attachment to music on a whole different level compared to technologies, which are replaceable and in most cases just tools to get things done, like listen to music.
Anybody who knows Apple wouldn't expect anything other than Beatles from yesterday's tease.
Here is one interesting bit from the nut-shell: "We are also interested in other non-traditional ways an embeddable Ruby web app server might be useful for native app development."