This doesn't necessarily prove that Duke University lowered the bar for black applicants, largely because the SAT is one of several admissions criteria used by U.S. schools. Any fair comparison would control for GPA, essays, extracurriculars (that's a big one in America), AP scores and so on. It makes no sense to just take the average of SAT scores, ignore everything else, and conclude that there is necessarily some covert affirmative action taking place.
In any case, it's not really news that U.S. universities, especially private ones like Duke, try to diversify any given class, in more ways than one. Ever heard of 'legacy admissions?'
Again, even if this was true, it's not a matter of official policy by which this is being done and, in this case, refers to discrimination on the basis of financial desperation, which hardly amounts to the ethnicity-based affirmative action that you claimed in your OP.
It should also be mentioned that there is a fixed number of places for Home/EU and a (smaller) fixed number of places for international applicants for most courses; a quick look at university course pages will show you the number of places available on that course for the following academic year. So it really isn't a case of discrimination against Home/EU applicants because they're separated from internationals in the admissions process (i.e. the internationals can only compete for the set number of international places, not the Home/EU places). Furthermore, whether this constitutes discrimination or not depends on whether these applicants were doing international A Levels or not.
It's a case of corruption, not misguided official altruism towards ethnic minorities, as you've stated in the OP. The reason why I asked you to mention which universities you were referring to is because all applications to UK public universities (which is to say, virtually all UK universities) have to go through UCAS, which goes to quite some lengths to prevent affirmative action of the kind that you're talking about.
Given all this, I don't think that any of this substantiates your earlier claim about affirmative action (and given that we're on a predominantly British website, I was genuinely expecting you to mention some examples of UK universities that officially, and for the reasons that you've claimed, discriminate in favour of ethnic minorities -- which aren't necessarily equivalent to international applicants given that plenty of international applicants are from 'white countries', so to speak).
The financial woes of British universities (and the resulting corrective measures) are a different issue entirely to the one that this thread is about.