Looking at StatelessClusterProxyFactory, it appears that the
default load balance policy for SLSBs has changed from EJB2.
For EJB2s it was Round Robin, whereas EJB3 seems to define
it as Random Robin:

Clustered clustered = (Clustered) ((Advisor)getContainer()).resolveAnnotation(Clustered.class);
...
if (clustered.loadBalancePolicy() == null || clustered.loadBalancePolicy().equals(LoadBalancePolicy.class))
{
lbPolicy = new RandomRobin();
}
else
{
lbPolicy = (LoadBalancePolicy) clustered.loadBalancePolicy().newInstance();
}

I can't see a reason for us to change the default in between EJB versions.