Another benefit is that as your internal userbase changes, you can revoke access from a single point and be reasonably assured that you've mitigated risk, which is something you only get with individually-secured services if you have a reliable directory system.
A problem with individually-secured ops/support systems is that most 3rd party code is not ready to be securely deployed Internet-facing.
Both approaches are totally workable, but the VPN approach is easier.