Well, Poser was out years before WinME :-) The fact that Poser 3 era bugs & quirks still exist tells you that they haven't updated a lot of code in a looong time and I doubt this is a high priority area for development. Really wild and total guess, simple avi's or image sequences may also be easier for the renderer to deal with than more complex video compression schemes.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken