Fraf, you are inferring and assuming a lot. The fact of the matter is I'm reading exactly what they wrote, they are a wholly owned subsidiary of GW. GW (to the best of my knowledge) has never explicitly divested themselves of FW rules/models and has not contradicted the statement included in the pdf. In fact I just got off the phone with customer service and the guy I talked to there stated that he agrees that there is no official statement from GW contradicting the verbiage at the top of the FW pdf "tau update" and there is nothing on the GW site indicating that FW models/rules intended for use with 40k are not official and should not be expected to be useable in an official 40k tournament.
The fact of the matter is that, until GW makes a public statement contradicting the verbiage in the pdf or divesting their rules from those put forth by FW then it should be taken as presented. Which is to say that it indicates it is official for use with 40k.