I think I have broken the code regarding this discrepancy between those who claim Priority Mail (at least some levels of it) have tracking even in international deliveries and others (including USPS clerks) who say only Express Mail has tracking.
Now this probably isn't really news to many, but it helps to have it spelled out for others. This actually came up when I had my wife take a media mail parcel to the Post Office to have it mailed without a prepaid label. I told her to get tracking for the package. She told me later that the clerks informed her that only Delivery Confirmation was available for the parcel, not tracking. I told her that I understand that, but it isn't really any different because I use Delivery Confirmation numbers to "track" packages within the U.S. regularly. I'm sure most of us do. When you go onto the USPS website, you put in your Delivery Confirmation number in the blank space labelled Track and Cofirm.
Technically, there is a difference between TRACKING and Delivery Confirmation service. With TRACKING, the parcel MUST be scanned at acceptance by USPS and again when delivered. There are generally more scans than that as the parcel moves along, but the only REQUIRED scans are at acceptance and delivery.
With Delivery Confirmation, the only REQUIRED scan is at delivery. USPS doesn't have to scan it at acceptance or at other spots along the delivery route. In general, they do multiple scans, but they are NOT REQUIRED to do them.
Thus, there is merely a slight difference in TRACKING vs. Delivery Confirmation. In your real-world experience, you won't usually see that difference. Nearly everything I send out is scanned in at my local post office except for media mail packages. They are usually scanned in at the regional processing center.
In any event, we generally really only care about Delivery Confirmation with overseas parcels since we usually aren't concerned that they will be lost in the U.S. Thus, Priority Mail is generally the more cost-effective method, but that may not always be the case. Individual cases may be different.
I hope that helps.
Here is a link with some info for those who want to research it.
http://faq.usps.com/eCustomer/iq/usps/request.do?create=kb:USPSFAQ&view()=c%5Bc_usps0301d%5D&varset(source)=sourceType:embedded