Something wrong with RAW editor?

Q:
Im using Photopaint 2014 Home and Student
When i browse my RAW pictures from camera, the Shutter Speed, says ex.1/800 s. (Canon 5D mk3)
On my camera, the shutter speed says 1/800 s.
When i OPEN the same photo, the RAW editor says Shutter Speed 1/790 s.

Why the difference. Sometimes its the aperture thats not correct.
Regards