Good explanation. But one thing that might not be obvious is that "b" is a moving target in the article (and in many cases where this technique is used), so usi

Good explanation. But one thing that might not be obvious is that "b" is a moving target in the article (and in many cases where this technique is used), so using your equation, moving "b" by one unit in a given frame will also move x(t) by one unit, causing it to feel a bit faster/more aggressive. Your final equation will guarantee that you will end up at (a given closeness to) the target at a given time, wherever that target might be, and however fast it might be moving away. Using the (poorly-named) approach in the article gives you a subtly different behavior, where the easing is essentially "reset" each frame. If you "run away" from the easing object at the right speed, you can delay it reaching you for an arbitrarily long amount of time, which has a different feel, and different practical consequences depending on the context. This is demonstrated in the "Follow the mouse" example in the article.