The two are not disconnected. Google is trying to guess what the user wants, and we're trying to guess what Google wants. Thus it's by many considered a good long-term practice to at least take the user in to consideration since that's where G is going. In a situation like local search, thinking about the user experience can give you heads up about where the SERPS are going - such as the increasing prevalence of universal search results.
I see what you're saying though, when you use the word "barrier" you're talking from the perspective of an SEO. But what I'm saying is that it depends on what SEO we're talking about - some predicted this by looking at where search was going and were able to capitalize on it and beat out, as you say, "big authority sites in several niches". For them it was not a barrier, but an opportunity.
And this was in response to the question posed in the title of your thread "Is local search at top of page a way to sell more Adwords"; businesses who could before only show up on the front page by buying ads (due to authority domains claiming the first page) can now show up through the 10-pack. Thus it decreases the need for using adwords for some, and therefore my answer is "no" - it's unlikely to be a trick solely to sell more adwords.
I think that's exactly what I'm saying. It was a rhetorical question because I thought the answer would be obvious. Here it is rephrased:
IMO, Google wants to show a business located near the user that's selling what they're looking for, rather than a site that has invested resources into link building and a perfectly optimized site. This is why we see an increase in 10-packs. Do you not agree with that?