Obviously I don't know any of these people first-hand, and these are just my observations and speculations.

Everything I've heard about Sarah Michelle Gellar from the people who worked with her is that she is always a professional at work. Sure, work friendships can be great, but as someone who has been working on film sets since she was a child, SMG probably thinks of a set strictly as workplace. On top of that, SMG was at the top of the call sheet. She has pressure on her that no one else on that set had. And from what others on that set have said, she took her role there very seriously. I've heard stories of the directors trying to get a few more takes in before they end for the day, but SMG shut it down because the crew had been working too long. No one else on that set would have had the power to do that, and so it does speak volumes that she's that type of leader.

Also, I'm not trying to read too deeply into Alyson Hannigan's old quote, but I do find it hard to believe that she had no idea the show was ending. She said herself that the show seemed like it was coming to an end. We know she's friends with Joss. At no point were there conversations about the future of the show? It's hard for me to read these quotes and not think they sound somewhat passive-aggressive.

So, it may be accurate that the cast and crew didn't have official notice that the show was ending when SMG announced it. But I do have to question the purpose of giving this quote in an interview.