Thanks for the comments:

Ronald: I agree that an int should be passed.  I understand your ctype comment as saying that an attribute error before making the call should be the only possible exception.

I should have explained the 'unrelated change' to the one entry box.  With the default size of 20, it no longer fits properly after the change.  Adding an explicit size was the easiest fix for something that is only present for test and demonstration purposes.  A better fix, which is not needed for this issue, would probably be to add a 'expand=True' or something, somewhere else.

I checked all the other panes on the settings dialog and the other major dialog boxes and found no problems.

Zack: I had the same question.  Now that I know that IDLE as a tk app *can* look 'sharp', the current fuzzyness is annoying.  I would not be surprised if it contributes to some of the negative opinions about IDLE.
  
Tk tries to look 'native' and this seems to be the main thing missing.  To me, the only obvious reason for tk to not use this setting as default
is that is can mess up spacing on current windows.  But to me, it definitely should be available.

I don't know if other systems have such a setting, or any need for such.  I will ask an someone who uses IDLE both in Windows and Ubuntu on the same machine to compare.

Serhiy: I have a space monitor and I believe my graphics card will allow me to attach one, so I may give it a try.
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The linked article recommends "that you set the process-default DPI awareness via application manifest."  I don't currently know what this 
means.  It appears that making one call before any tkinter calls is the right thing to do if any call is to be made.

The call does not appear to be available on Windows 7 or 8.0.