Can someone tell me when and where Bethesda announced that they were officially done supporting this game (and Fallout 3 if you know)?

Check the various gaming rags starting from about the time FO3 came out. Todd made the statement several times that I am aware of, in a selection of magazine articles.

Well I guess I'll just use the date of the last official patch. I don't have those gaming rags nor do I feel like scouring the internet for a Todd Howard interview. Again, you'd think this information is something that would be readily available on the official support forums, kind of like those EULAs, but I guess Bethesda does things differently. Maybe that's why I couldn't find their own online store's return policy either.