It is cool. There is no need for the image to 'coast'. You could land at the extrapolated end position immediately, just as page up or page down does not need to animate the scroll. Kinetic, as in animated method of scrolling, is meant to be cool.
Again, there are not just two ways of scrolling content. See pyqtoreader - it's faster and more precise than kinetic scrolling. Kinetic is just hero of the day, there are plenty other methods of scrolling (stylus based or other) that can replace it one day (given apple does a fancy implementation of them )