I can't answer Diane's question because I haven't used most of the cameras she asks about.
I should say, though, that in my experience, Nikon's color response quirks aren't limited to natural subjects. (But keep in mind that I'm comparing raw files in Adobe Lightroom, which could be introducing its own distortions.)
Here's a Panasonic G1 image:
And here's a Nikon D300 image from the same production:
Note that this is
after I've tried to adjust the images to make them appear as similar as possible! To me, the reds in the Nikon image seem more saturated and warmer; the Panasonic image's reds aren't as vivid, and pick up more of the subtle purple bounce off the floor.
As an off-the-top-of-my-head generalization, I'd say that the Nikon (again, as processed in Lightroom) seems to target colors that already are saturated and ramp up their saturation further, while the Panasonic seems to be more linear in its response to saturation. This makes the Nikon images look "punchier" and possibly more immediately appealing, while the Panasonic colors look more "natural" and subtle.
To be fair to Nikon, they provide lots of controls for adjusting the camera's color response, storing different profiles, etc. So it may be that they ship cameras set up to provide a vivid, appealing image when you try them in the store, and trust you to tailor the color response to your needs later.
Anyway, it's interesting to see different manufacturers' interpretations of how color should look... harks back a bit to the days when we'd choose from a raft of 50- and 100-speed color transparency films to pick the one that had the right "personality" for a particular subject...
[Note: If you examine the attached images, you'll find that the filenames -- "panasonic_example" and "nikon_example" -- are switched. The text above identifies the originating cameras correctly. Sorry for the mixup...]