1. Shallow depth of field (close objects in focus, far objects out of focus). Doesn't necessarily mean poor quality, but webcams have wide DOF, so you might associate shallow DOF with good quality
2. JPEG compression- I see more compression artifacts in the Nexus video. This isn't related to camera quality at all.
3. Sensor quality looks better to me. Details in the dark rear-view mirrow, more detail in the sand.
2. Agreed. But it seems like a lot more post-processing was done on the 4S video, which may have reduced the compression artifacts.
3. That scene looks like it was shot on an overcast day. Even with my Epic 4G it would not be difficult to get that level of shadow detail.
From the vid: "I did give this footage a slight grade with the 3-way colour wheel in Final Cut."
I'd say it's the change in colour balance that gives it the feeling you're describing, it certainly feels that way to me.
I do agree that cameras are getting pretty good. Once I get my 4s, I'm planning on spending a few hours learning videography (or whatever they call it).