Re: Context
Yep - back in the early days of Adsense we got a jolly good income from embedding ads on our websites taking advantage that the content was matched to ours. So the user aleady had an interest - and clicked.
Then they changed to the content 'matching' the user not the website so often producing stuff that was the antithesis of what the containing website was about. Our revenue slumped so much and as the contrasting content devalued our sites we exited the Adsense business.
The mystery is how this made Google richer.