Topic BlizzCon 2013...?
They probably didn't do Blizzcon 2012 because they didn't have enough stuff to show us.
2012: Mop was almost out, so no surprises. SC2 zerg expansion was already out and so was D3. They were basically between projects and starting on new things about the time Blizzcon would of been on.
2013 we should have a sneak peak at the next SC2 expansion, the next wow expansion and maybe even a sneak peak at whatever project titan is, not to mention potentially a D3 expansion sneak peak. All that stuff would have 2014 releases spread across the map.