The real reason there was no Android 4.3

Some reports have surfaced that Google intentionally left out an announcement for a whole new OS update to demonstrate that they can update the core features of Android through Google Play and new develoer tools and thus hone in on platform fragmentation.

Is is reported though that Android 4.3 will be released, alongside a white nexus 4, come June 10.

It's unlikely that they will have any announcement at I/O about it, most likely either a standalone event in June or a simple press release a la Nexus 4.

Source: http://goo.gl/44p37