From a quick test with that code snippet, it looks like the 2d fiducial displayable manager is not detecting that the fiducial has been added and that it needs to be displayed (the fiducial is showing up fine in 3d for me on a linux debug build after the initialize call), until there's a post initialization change in the fiducial's location.
Part of the problems is that initialize doesn't actually set any of the points, and the 3d manager defaults to setting the glyph at the origin, while the 2d one just doesn't display it. Setting the fiducial coordinates is required, but somehow that's not triggering an update.
On the mailing list you mentioned a work around, could you let me know what you did?

• the workaround I am using right now is:
  fiducialNode.SetDisplayVisibility(0)
  fiducialNode.SetDisplayVisibility(1)

Digging back a bit in the bug archives, something similar had come up previously in bug 3164. If I try this order of python calls, the fiducial shows up in all the viewers for me:
f = slicer.vtkMRMLAnnotationFiducialNode()
f.SetFiducialCoordinates(0,0,0)
f.Initialize(slicer.mrmlScene)

Can you check to see if that works for you?

Yes this does work, maybe the initialize function could set the fiducial coordinates to a default [0,0,0]...

The annotations are getting deprecated for the Markups module, it makes the most sense right now to just provide a utility method on the logic to add a new fiducial, checked in as svn 22205[1].

fidID = slicer.modules.annotations.logic().AddFiducial(10.0, -50.0, 8.8, 'P1')
f = getNode(fidID)

[1] http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=22205