How spinal manipulation might reduce pain

An increasing number of studies are investigating the pain reducing effectiveness of spinal manipulation, and are positing the various mechanisms that might account for it.

Here is an example of a trial doing just that. Note, however, that most osteopaths will hardly ever manipulate to directly relieve pain - rather we will attempt to improve function through manipulation, which then relieves pain as the body or spine starts to work better.

I'm not sure scientific researchers appreciate this distinction?