That note is not in the first or second printings, but was added to the third printing, released 2010. So, if you bought the PDF last week then whoever sold it to you is not serving the latest edition.
Coincidentally I discovered last night while updating TW errata that this change had been made, but was not recorded in the errata. It is in the errata thread however, and I've now added it to the internal TW errata document.