[Pacemaker] "Using ldirectord" page question

[Dennis Jacobfeuerborn]

Hi,
I'm trying to set up a redundant load-balancer using pacemaker and
ldirectord and found an example for the configuration on the following page:
http://www.clusterlabs.org/wiki/Using_ldirectord

What I don't understand is the following part:
"This gives you the virtual IP address and ldirectord running together in a
group (ip-lvs) on one node, and the same virtual IP address assigned to the
loopback address on all other nodes. This is necessary to make the routing
work correctly. "

Why is the configuration of the IP on the lo interfaces necessary for routing?
As far as I understand is the VIP only needs to run on the active node that
is also running the ldirectord daemon. Once the failover happens both move
over to the new active node and the setup should continue to work as
before. Is there something I'm missing here?

Regards,
  Dennis