If you use GATEWAY= in ifcfg-ethX (e.g. netconfig does this), 
duplicate default routers will be added (one with metric 1, one with metric 0), 
unless you have the following line in /etc/sysconfig/network:

GATEWAY=

 .. This is caused by the following in /sbin/ifup:

---
    # this is broken! it's only here for compatibility with old RH systems
    if [ "${GATEWAY}" != "" -a "${GATEWAY}" != "none" ]; then
        route add default gw ${GATEWAY} metric 1 ${DEVICE}
    fi
---

Happens in both RHL62 and RHL70.