Service object inconsistency?

Does anyone know why these don't work?

services = client.list_services()

# Why do only some of these work?
print services[0].id           # Works
print services[0].name         # Works
# print services[0].version      # Doesn't work
# print services[0].versions     # Doesn't work
# print services[0].updated_at   # Doesn't work
print "-----------"

# But all of these work fine
print services[0]._data.get('id', None)
print services[0]._data.get('name', None)
print services[0]._data.get('version', None)
print services[0]._data.get('versions', None)
print services[0]._data.get('updated_at', None)