Tim Cook said that Apple will double down on secrecy on products in May 2012 . This was after a couple of years where almost everything that Apple was going to release was revealed by outside sources prior to Apple revealing them. Apple was losing its power to control the future product information. Apple traditionally (at least whenever Steve Jobs was there) always wanted to be extremely secretive and wanted to control any piece of information about the company that goes out. This legendary secrecy came from a belief that people like surprises, I mean like how you feel on the Christmas Eve. Remember the original iPhone launch, not much was known prior to the event and the hype was crazy.
For whatever reason there were a lot of leaks prior to the Apple events in the recent years and there was no more a surprise factor that existed prior to any Apple event, the worst was of course the iPhone 4 bar incident. But the recent WWDC 2013 suggests a possible change in this trend. As far as I know, there was a lot of talk about iOS going flat(ter) prior to WWDC '13, but that was it on iOS, nothing more. Probably a very blurry screenshot of the home screen and surprisingly accurate icons rendition, but again only the night before. Though Mac Pro was expected (not through a leak but mostly through Apple itself) while iRadio rumors were mostly generic, with no particulars. Not that anyone other than me cares about Mac OS X, but Mavericks and none of its features trickled out in advance. Retina Macbook Airs were expected, did not happen (though some sane guys repeatedly warned against such expectations, citing battery technology limitations). Lighter Macbook Pros, Apple TV updates (either software or hardware), etc. were all predicted, but nada, nothing was announced. Over all, this WWDC (2013) felt like Apple succeeded in maintaining almost all the announcements a secret prior to the event. If this is a one off thing or a continuing trend as a result of Apple's improved efforts, is too early to tell.