So why does Canon 5D Mark II have a better video quality than Canon 60D?

Question

Assuming that Canon 5D Mark II and Canon 60D both have the same processor, DIGIC 4 (single), why does the former shoots a better quality video? Better quality I mean the technical aspect, the video/compression itself.

Let's ignore the visual aspect like more shallow depth of field, for example.

I know 5D is a full-frame, but the video is 1920px wide. The 60D shoots 18MPx, which scaled down to 1920px wide should still look almost the same as if shot on full-frame initially, right?

Therefore, and this is my point:

UNCOMPRESSED INPUT -> DIGIC 4 -> OUTPUTTED VIDEO

If we exclude the depth of field and a better ISO handling from our equation, it's possible that the uncompressed input is the same on both cameras, right? Then, it goes to the digic 4 processor to be compressed, which is the same on both cameras. Yet, we end up with a better quality video on one of those cammeras. Why?

Answer

The 5D Mk2 has a far larger sensor (because its a full frame camera) and more pixels. My assumption would be the camera scales down the input to 1920x1080 so having more uncompressed data allows it to give a higher quality output.

If Andres's comment about it skipping lines whilst taking video is right, then the improvement in quality is more likely down solely to it's lower pixel density. A lower pixel density means a bigger area per pixel, which means more light per pixel, more light per pixel means less amplification is required (amplification increases noise also)

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