Firstly there are a couple of general reasons raw and JPEG images differ in size, and raw differs from the actual number of pixels on the sensor:

Whilst JPEG image dimensions don't have to be multiples of 16 (or 8 if not using chroma subsampling) it is more efficient to do so, as it allows you to rotate the images without re-encoding (lossless rotation). So that can account for a small image size difference, as you say.

Even raw image sizes typically differ from the actual number of pixels as most sensors have strips masked pixels (that receive no light) down each side in order to detect banding issues with uneven amplification. Further, the size you see in your raw viewer will differ from the actual raw data as some image processing operations use a form of averaging which doesn't work at extreme edges (because there's no data beyond the image to use when averaging) so they get cropped off when the image is viewed/converted.

Secondly the Panasonic Lumix LX3 and LX5 have a different sensor design to most cameras, which is partially responsible for the difference in coverage between raw and jpeg you are experiencing:

The maximum 16:9 image size is actually wider than the maximum 4:3 image size. You would expect them to be the same width but different heights.

This is because they've made the sensor a bit wider for 16:9, employing a non rectangular design and it's pushing the very edges of the lens image circle, this explains the vignetting and CA you observe with the raw. This diagram shows the irregular design: 



As John Cavan suggests, the JPEG image pipeline is doing some correction, including barrel distortion correction, given that 24mm equiv. is very wide for a compact, and the sensor is pushing to the very edge of the image circle. 

Barrel distortion correction makes straight lines straight again, but will cause the image edges to bend in response. In response to this the correcting transformation enlarges the image slightly and crops to get straight edges again. 

Can you see any differences in the appearance of straight lines between the raw and JPEG? It might be quite subtle but get revealed if you overlay them. 

Why is the pixel count of RAW images from the Panasonic LX5 slightly larger than the generated JPEGs?
I am in the process of hanging drywall for my basement.

Due to the length of the walls there are a couple situations where I could either hang the sheets to have a single butt joint.. or to have 2 tapered joints. Which one would be better for the mudder? I am planning on hiring out the mudding but have not hired anyone yet to ask. thanks.
