Hi John,
Not really adding much, but my views are;
a) Only a few, close range shot, subjects (e.g. Colin's example) can hope to be 'good enough' without any PP in 'neutral' jpg (and even then there is the default jpg sharpening, etc. applied compared to RAW)
b) Anyone shooting jpgs using scene modes or film profiles is undoubtedly applying 'PP' because most scene modes on modern cameras will not only set appropriate iso, aperture and shutter speed, but also change things like saturation, offset white balance, etc. to achieve a better result for that subject
c) Anything shot at a distance (e.g. landscape or wildlife) is going to have atmospheric degradation that really needs to be corrected, it is impossible to 'get it right in camera'!
One could certainly argue the shot should not need horizon leveling in PP, but really, there are so many other variables and occasions when PP is necessary to overcome limitations of what we have available (e.g. shooting panaoramas because we don't have the UWA lens) that really Frank's post (#3) states it well - you'd have a very limited (and boring) portfolio without PP.
Cheers,