The Bezier easing demo is now online. It only illustrates ease-out for a few ease types, but it should be enough to get the idea across. The following screenshot illustrates the difference between natural and arc-length parameterization for a cubic Bezier curve with cubic ease-out.
The red marker illustrates application of the ease without arc-length parameterization. The green marker illustrates proper easing with arc-length parameterization. Although motion along the top curve appears to be eased, the motion is incorrect. Worse, the actual velocity along the curve is a function of geometric constraints.
The online demo may be viewed here. The page includes a link to download Singularity. The demos folder includes the MXML file for this demo which can be modified to test different easing methods as well as ease-in.
The Algorithmist 
Interesting – never thought about this.