I can't answer your question but in the case of the package that you sent USPS...what country did you send it to and which service did you use? First class international, Priority flat rate envelope and small flat rate boxes only have tracking outside of the US for certain countries.
You can set up your own Fedex account and ship that way. When buying Fedex through ebay there are a lot of complaints about Fedex surcharges being added after the item has been sent so you might be better off using your own account.
However...unless you are using an express service, if Fedex has to collect taxes and/or duty from the buyer, they will also add brokerage fees and those can add up. I know that in Canada, I probably wouldn't buy from a seller in the US who uses Fedex as they are obligated to charge tax and duty. When the postal service is used, it's more likely to go through customs without any extra charges being added.
