Biden says US forces would defend Taiwan if China invaded

As I understand it, this is a significant change in American rhetoric, which has always been deliberately, strategically vague on the subject.

I'm not sure how much of a difference it makes, or why they'd make such a change right now. I would imagine it's a response to the notion that China has been watching the US send money and arms but not troops to Ukraine, though it seems to me that the situations are not sufficiently parallel for anybody to jump to that conclusion.