http://www.bungie.net/en/News/News?aid=12133

So, all of the game modes and story that feel like they're missing from the game are going to be released over time to keep people playing. Not a terrible strategy, but again, frustrating that we can't just have the stuff we thought we were buying at launch.

It's not that I'm mad. I'm excited there's going to be so much more to play. I just wish Bungie hadn't been so vague about their plans. I think it had an effect on people's expectations.

Public Events will erupt from the skies over your favorite destinations with greater frequency.

This. More of this.

Yeah, I thought I was going crazy. I have only seen a single public event on the moon so far... I loved all the public events from the beta