Or should I be asking why is it slower encoding an AVI?

I am finding that CCE 2.5 encodes a .d2v file from a DVD rip at a speed of approx 1.1 -1.3 but encoding a DV AVI file it runs at approx 0.55-0.64.
Both instances are frameserved using AVISynth and I have tried using the SimpleResize and BiCubic. All the CCE settings are the same and I am creating SVCDs.

My best guess is that there may be less effort required required from the encoder to re-encode a DVD MPEG2 compared to an AVI?