I am not sure what you mean by "real optical flow". It is simply a technology that is used to analyse motion from one frame to the next or identify the same objects in different positions in two or more images. It is used in some of Shake's retiming and deinterlacing tools, Shake's smoothcam node, Stitcher, Furnace and a host of other applications. It is also used in the encoding process of MPEG's. It is also known as 'motion estimation'.
Rumour has it that the wraith world effect in lord of the rings was achieved in part by analising footage of fire using optical flow. It is likely that the resulting motion vectors were used to drive a complex particle effect in houdini or maya. However it was done, it is great R&D.
I dont personally see how optical flow could be used to drive an automatic morph between two images but it is an incredibly useful technology and people are finding new applications for it all the time.
Shake is not made to be a one click solution. The morpher in Shake isnt meant to be simple. It is meant to provide the tools so that artists have the controlability that they need. If Avid's fluid morph is working for you, why not use it?