pyqgis - QGIS layer tree API returns only groups and not layers

I am trying to use the QGIS python API to read out the groups and layers in a QGIS (2.4) project. Here is a code snippet from my script, which is run from a shell, not from the QGIS python console!

from PyQt4.QtCore import QFileInfo
from qgis.core import *


proj=QgsProject.instance()
proj.read(QFileInfo("/var/qgis-projects/testproject.qgs"))

print "QGis version:"+QGis.QGIS_VERSION
print "Project title: "+proj.title()
print "Project tree root children:"
root=proj.layerTreeRoot()
for node in root.children():
    print "- "+node.name()+" ("+str(type(node))+")"

It prints the following when I run it:

QGis version:2.4.0-Chugiak
Project title: This is my project title
Project tree root children:
- Field Data ()
- Aerial Photos ()
- Other Maps ()
- Model Results ()

Only QgsLayerTreeGroup objects are returned but no layers (QgsLayerTreeLayer objects), even though I also have two layers in the project root. When I open the python console in QGIS while I have my project open and run:

QgsProject.instance().layerTreeRoot().children()
[, , , , , ]

This does return the QgsLayerTreeLayer objects for my layers that I'm after. How come there is a difference?

Edit: I'm trying to run my python script from a shell, not from the QGIS python console.