Is it common for vertical joints to not be filled?
No this is not common.  In some areas it might even violate code as there might not be fire separation.  

However to say does this mean anything structurally... who knows without full details of the building.  Unless you live in a third world country I doubt that there would be a building with more than 10 stories that relies on cinder blocks at all for support.  Most interior walls in high rises are made to be taken down and moved if needed.  Most buildings rely on exterior walls and key points usually in the center square of the building. 

Why is there a gap in yours?  Maybe it is for expansion - but then this should have fire rated caulking.  Maybe the workers were lazy and knew it would be covered... who knows.  Should you be worried?  No.

Note:  You should not be worried about the building falling over.  However if there is smoke coming in yes you should be worried about both your health (air quality) and fire will spread faster (well I would gather that it isn't the fire itself, it seems the smoke from a fire could spread and be hazardous easily in your situation).