I might be missing something myself, but isn't JPEG a compressed format itself? If that were the case, wouldn't fiddling with the quality parameter result in different levels of compression?

A quick scan of google didn't show me anything to set "jpeg" apart from "compressed jpeg" - most links were describing jpegs as compressed when compared to formats such as bitmap.

"All you need is ignorance and confidence; then success is sure."-- Mark Twain