The sharpening process uses different algorithms. When the picture is sharpen, some artifacts of sharpening process could become visible: ghosting, echo, amplified noise, but the most visible consequence of sharpening is stronger light-dark line on contrast edges. You can find a sharpening artifacts described on the page of Computer sharpening.

Picture data:

Reduced to

14%

Resampling process

Anti-alias

Compression

30 steps

Original image data:

Type

fine JPEG

Resolution

2560*1800

File size

1257 KB

Image size/72dpi

903 x 677 mm

Focus

200 mm

Aperture

9,5

Shutter time

1/30 sec

ISO

100

WB

Daylight

Color

0

Intensity

0

Contrast

0

Sharpness

Soft

Default settings

If you take a close look on magnified pictures taken with different sharpness settings, you'll find a probability that default sharpness setting in camera is 'soft'. This could be true. The big problem of camera's CCD is low resolution ability which brings out dim pictures. The original RAW file is recalculated so final sharpness depends a little on quality of interpolating program. Thus, the basic level of sharpness is already set in camera before the image data is recorded onto disk.
 
This could be found when you compare real resolution charts of different cameras with same resolution source, when the tests shows different final resolution results.

Sharpness