Nick, I am afraid it is not me who has misconceptions here.
A CoC can indeed have something to do with printing (as well as DOF). Just take a look at the Wikipedia page on Circle of Confusion where they say
"The common criterion for “acceptable sharpness” in the final image (e.g., print, projection screen, or electronic display) is that the blur spot be indistinguishable from a point." Here is the link:
http://en.wikipedia.org/wiki/Circle_of_confusion
In addition, even Alpa does not agree with you with regard to your claim that CoC is independent of any device. Contrary to your belief, Alpa indeed finds CoC as being dependent on device. For example, just take a look at their spreadsheet here where they associate various CoCs for different devices:
http://www.alpa.ch/dms/products/tools/alpa-comparable-focal-length-calculator/ALPA_CFL_Calc_V217B.xls
If you go back and think a little harder about the previous example I just gave you (with the printing of the 2D resolution chart of zero DOF), you should be able to see how the confusion between DOF and print viewing resolution arises due to the misunderstanding of the different meanings of their respective CoCs.
I am pretty comfortable with my understanding of what a CoC is. And I'm pretty sure you are also clear on its empirical meaning in the sense that as an image 'point' becomes pregressively defocussed it eventually becomes recorded as a spot or disc (Airey Disc) covering a certain number of sensels. Once it covers 2x2 sensels it is usually considered degraded or 'out of focus'. This is part of the definition surrounding diffraction error etc but will serve here to make sure we are all on the same page regarding what a CoC is in its most basic form.
Your Wikipedia reference confirms everything we (Sheldon, Bart and myself) have been trying to explain, please consider the following section, in particular point two and three:
"The CoC in the original image (the image on the film or electronic sensor) depends on three factors:
1 Visual acuity. For most people, the closest comfortable viewing distance, termed the near distance for distinct vision (Ray 2000, 52), is approximately 25 cm. At this distance, a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2 mm in the final image.
2 Viewing conditions. If the final image is viewed at approximately 25 cm, a final-image CoC of 0.2 mm often is appropriate. A comfortable viewing distance is also one at which the angle of view is approximately 60° (Ray 2000, 52); at a distance of 25 cm, this corresponds to about 30 cm, approximately the diagonal of an 8″×10″ image. It often may be reasonable to assume that, for whole-image viewing, a final image larger than 8″×10″ will be viewed at a distance correspondingly greater than 25 cm, and for which a larger CoC may be acceptable; the original-image CoC is then the same as that determined from the standard final-image size and viewing distance. But if the larger final image will be viewed at the normal distance of 25 cm, a smaller original-image CoC will be needed to provide acceptable sharpness.
3 Enlargement from the original image to the final image. If there is no enlargement (e.g., a contact print of an 8×10 original image), the CoC for the original image is the same as that in the final image. But if, for example, the long dimension of a 35 mm original image is enlarged to 25 cm (10 inches), the enlargement is approximately 7×, and the CoC for the original image is 0.2 mm / 7, or 0.029 mm.
The common values for CoC may not be applicable if reproduction or viewing conditions differ significantly from those assumed in determining those values. If the original image will be given greater enlargement, or viewed at a closer distance, then a smaller CoC will be required. All three factors above are accommodated with this formula:
CoC (mm) = viewing distance (cm) / desired final-image resolution (lp/mm) for a 25 cm viewing distance / enlargement / 25
For example, to support a final-image resolution equivalent to 5 lp/mm for a 25 cm viewing distance when the anticipated viewing distance is 50 cm and the anticipated enlargement is 8:
CoC = 50 / 5 / 8 / 25 = 0.05 mm
Since the final-image size is not usually known at the time of taking a photograph, it is common to assume a standard size such as 25 cm width, along with a conventional final-image CoC of 0.2 mm, which is 1/1250 of the image width. Conventions in terms of the diagonal measure are also commonly used.
The DoF computed using these conventions will need to be adjusted if the original image is cropped before enlarging to the final image size, or if the size and viewing assumptions are altered."
(My emphasis)
That's all we are saying, if you enlarge the image past it's original size (ie view or print it) you need to recalculate the DOF as the assumed CoCs are no longer valid.
Your CoC chart from Alpa merely defines the CoC of the device at the
native size of the image, whether a piece of film or a digital sensor, not when it's enlarged. I admit my 'device independent' comment was misleading but the above reference, provided by you, should make my (our) meaning clear.