Hi Curious,

re:
> Also why the fillet does not work on the purple model?

The thin sharp meeting edges at the bottom with surfaces smooth at the bottom is a difficult fillet case, there is some discussion here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=9512.2

You can use the technique there to get most of the fillets for yours but the skinniest area of yours would need some manual trimming and surfacing to fill in.

- Michael