Most albums mentioned on the Where Are They Now? site probably only sell in the thousands and we rarely get to hear any definitive sales figures. I was told Survival & Other Stories sold about 1500 copies on the Anderson Wakeman tour, but that has not yet been available anywhere else. Thus, in the absence of data, it's hard to know which albums have sold better.
However, we can probably say that one of the best-selling of 2010 was Asia's Omega. That's because Omega made various national charts: #29 in Japan and the top 60 in Germany, Sweden, Norway and Switzerland, plus #13 on the UK indie chart. It also did well on the Amazon (US and Canada) and CD Universe sales charts. So, Omega, the best-selling album by a Yesman... well, it would be were it not for Trevor Horn.
Robbie Williams' In and Out of Consciousness: Greatest Hits 1990–2010 includes 3 songs from 2009's Reality Killed the Video Star produced by Horn and two new tracks, one of which, “Shame” with fellow Take That member Gary Barlow, was also produced by Horn and released as a single. "Shame" went #2 in the UK, #1 in Hungary, #4 in Europe, #7 in Italy, #11 in Germany and so on. It was certified Silver in the UK (i.e. 60k). In and Out of Consciousness: Greatest Hits 1990–2010 made #1 in the UK, Germany, Austria and Europe; selling 120k copies in the UK in its first week (the second fastest selling album of 2010 in the UK). It also made the top five in Italy, Spain, Australia, the Netherlands, Belgium, Denmark, Portugal, Switzerland, Ireland, Croatia. It was the 40th best selling album of 2010 in Europe. It has now gone Platinum in the UK (300k), and Gold in Austria (10k), Belgium (15k), Germany (100k), Italy (30k) and Portugal (10k). So, that's at least 465,000 certified sales.
That's the highest sales for a project by any Yesman, but not for any project featuring a Yesman. To explain... "In High Places" was a song by Mike Oldfield with Jon Anderson, and a section of Jon singing has now been sampled by Kanye West for his latest album, My Beautiful Dark Twisted Fantasy. That album made the US #1, selling 496k copies in its first week, and 822.5k in its first five weeks. It made #1 in Canada with first week sales of 29k. It made #16 in the UK, and went Silver. It made #6 in Australia, and went Gold (35k). It also made the top 20 in the Germany, Denmark, Norway, Netherlands, Switzerland, Sweden, Ireland and New Zealand. So, that's at least 886,500 sales, 886,500 people hearing Jon sing!
However, if we talk about audience rather than sales, then Trevor Rabin probably wins. He did the music for "The Sorcerer's Apprentice". The film has grossed $225,363,077 at cinemas and in DVD sales. I don't know exactly what that means in terms of the number of people seeing the film, but perhaps something of the order of 10 million have heard his score.