I have noticed that my Canon Powershot G11 tripod mount is more in the center of the body of the camera and not aligned with the lens/sensor. Is there a reason for this? My concern is that as I rotate the camera thru the horizontal axis, the lens/sensor is not the the center of the imaginary circle. I can't accurately explain my concern, but the fact that the lens/sensor is not the focus, that the focus of the circle is offset is bothering me.
To answer your question directly, there isn't a photographic reason why it would be shifted from the optical axis, other than packaging, electronics, weight placement, or other industrial design compromises that are specific to that camera or model line.
But to fix the issue so that the optical axis intersects the axis of panoramic rotation, the easiest solution is to buy a camera-specific adapter plate to mount your camera into a tripod clamp mount. For instance, the Acratech quick release plate for Canon G11:
The intention of these plates to is stay mounted on the camera long-term. Note that as opposed to generic QR plates, the screw for the plate is very close to the right edge. That's because the G11's battery door hinge is close to the tripod mount socket on the bottom of the camera. This specific plate allows you to remove the battery without removing the plate; few generic QR plates, if any, will be as accommodating. Once mounted to your G11, this plate is centered under the lens.
Of course, the plate is useless without a corresponding QR clamp on your tripod. Search your favorite online retailer for "Arca Swiss clamp" — they can be found for as little as 10 USD.
This is possibly to achieve the most natural balance on a tripod(*). If you are using a ball head, to have the center of gravity over the head reduces the strain, and a small tripod, this also reduces the changes of the tripod tipping over. Of course the balance along the lens axis may be harder to achieve, but even then you have one single axis to consider which makes things easier.
This hypothesis can be easily checked: try to balance the camera along some hard edge and see if the tipping point is when the edge in on the tripod mount.
(*) As far as I can tell, on interchangeable lens cameras (DSLRs or mirrorless) the tripod mound in aligned with the axis of the lens, because the lens is often heavier than the camera.
The tripod mount on the Canon G11 is located adjacent to the battery door for convenience and structural stability.
I examined seven compact cameras (chosen for ease of access). Five of them have the tripod mount adjacent to the battery door. All of them have screws located near the mount.
I examined three mirrorless cameras (also chosen for ease of access). Two of them also have the tripod mount adjacent to the battery door.
It's an easy place to put the mount because the hinge of the battery door already needs to have underlying support and screws. Putting the tripod mount elsewhere would require the use of additional support and screws.
Here's a photo of the bottom of the Canon G11 from Ken Rockwell's review: