That is not true.
Not all Oakleys are made in US. Over these few recent years; especially metal made type frames are now made in china, which are all authentic Oakley.
They have pushed much production to China.

You will see CHiNA stamped in most Plaintiff, frogskin LX too!
And most recents 2013 release they dont even stamp "Made in USA" anymore. Just "USA"

The very simple #1 rule to find out if yr Oakley sunglass/spec is Original & NOT fake is to:-

1. Scratch the SKU/white lettering on the inner stem.
  - if lettering comes off = 100% fake oakley.
2. All ori oakley comes with microBAG with a drawstring, not just a black piece of cloth