Could the slight delay in release simply be due to legal issues such as scrubbing patent issues and verification that OSS code isn't infringing?
Update: +1 to everyone thinking 'man, I bitch about google sometimes, but this kind of thing is totally legit and awesome'
Google has generally been good about releasing emulator images prior to releases, though usually it's only a few weeks. Luckily, it takes time for Android versions to achieve large market share, so any bugs can be squashed before it's a big problem.