"So I understand, low paid clicks often relate to auto-placements whereby advertisers may conduct some kind of test-marketing and media pre-selection process."
Yes, smart ones do. Contextually matched sites / pages are the way advertisers can scale their efforts - it's too time consuming to JUST search for pages and sites to hit. Contextual matched targets (Auto Placements) are the easy way to discover sites that convert. But, not all advertisers are rational, smart, or thorough. Many just setup contextual targeting and never do anything more. Others who work a little harder, might search for Managed Placements at the beginning. The best results come from doing both of these things contextual Auto Placements and best-guess Managed Placements, then SEE what happens and react to it.
Contextually matched <> converting.
But it's a good starting point.