Right. Because Microsoft wouldn't stop making Mac:Office just because it might inconvenience Mac users.
Come on. Apple is smacking Microsoft right in the face. They are saying, "Screw you, we don't need you anymore. Take your toys and go home." They are saying, "We don't need you to keep making Office for us anymore." This is a significant shift since the late 90's when keeping Office on the Mac was a huge deal for Apple. They basically begged Microsoft to keep making Office. Now they're launching competing products against Office? That's a sign.
And I'm betting that Microsoft never releases another major version of Office for the Mac ever again. Why should they compete with Apple for a market that's 3% of their current market? They're not going to fight for it; it's not worth their time.