"The Python x.y docs describe the Python x.y language and stdlib, minus Idle (and turtledemo). The Python x.(y+1) What's New describes the delta between Python x.y and x.(y+1) in a user friendly and relevant way."

I don't understand "minus IDLE (and turtledemo)".  They look documented to me:
 
https://docs.python.org/3.4/library/idle.html
https://docs.python.org/3.4/library/turtle.html#demo-scripts
https://docs.python.org/2.7/library/idle.html
https://docs.python.org/2.7/library/turtle.html#demo-scripts

"As near as I can tell, the general NEWS file is not easily accessible."

The URL for the NEWS file for each release is included as the "Release Notes" link for each release on https://www.python.org/downloads/.  For Py3 releases since Python 3.3, a formatted HTML version is available, at urls like:

https://docs.python.org/3.4/whatsnew/changelog.html#python-3-4-1

For all current releases, include Py2.7.x, a raw text version is available at urls like:

http://hg.python.org/cpython/raw-file/v2.7.8/Misc/NEWS

I believe it has been suggested before that the NEWS button could open a browser window with the appropriate release-specific URL from above rather than opening a Tk window with news.txt.

"What's New 3.4 has only this about Idle: [...]"

These sections are not immutable.  If the section for a previous release is incomplete, you can update it in the current branch(es).

Rather than duplicating information between IDLE-specific files and the normal Python What's New and NEWS documents, wouldn't it better to just get it done well all in one place?  This doesn't have to be difficult.

In any case, this seems to be pretty much a duplicate of Issue17506 and probably Issue21621.