I think this Admin-ajax.php is just another example of the completely unprofessional implementation of new features by Wordpress.org that CRIPPLE thousands of websites.
Why not implement these as an option?
In v3.9 we lost features from images and widgets with code stopped working.
Most professional IT people know about change control, that you allow for training, you do not implement things that mess up people's sites, instead you make them an OPTION in SETTINGS.
We should not have to HACK code and now they upgrade point revisions automatically to fix the mistakes, so we mow have our sites going back to wordpress to update code without any authority from the site owner.
When those updates screw up our sites we look bad
Again we have tp hack code to disable this madness