There were two major standout points to me in the article. The first was that the main engines (SSMEs) were replaced so that the originals could be used for the next generation system.

The other thing that's piqued my curiosity is that once drained of fluids, the shuttles could never be powered on again. Not just "can't be certified for flight" or even "engines can't be safely fired", but a complete inability to even power on.