Hmm this is a very interesting topic (It should be a thread of its own). I think what's happened with the Jin fellow is that in the past, he's only shipped unregistered priority.
Whilst ems is the fastest with the most informative and reliable tracking info, you can achieve almost the same level of service if you go with registered priority.
I'm pretty sure Priority as a stand alone service only provides the acceptance date and delivery date "tracking ID" - and about 70% of my packages that have been shipped this way have never generated a delivery date on the USPS website, despite being delivered. I even tried checking again 3 months later on one of my packages and it still didn't update the status to delivered.
I've had medium sized transformerland orders shipped via both First Class and Priority but decided to pay the additional $9.99US (each) to register them. Both of these provided step by step tracking almost as good as ems.