Judging a biography by its cover

I've become a little more sensitive to cover images since struggling to find one for my own book--where's a clean and zany Victorian engraving of Joan of Arc when you need one?--and so I couldn't help noticing what happened to Michael Turner's new biography of William Pitt the Younger after it crossed the Atlantic. The UK cover combines the Karl Anton Hickel group portrait of the House of Commons with what looks like the AWOL portrait by Thomas Gainsborough (copy here). In contrast, the US cover keeps Hickel, but jettisons Gainsborough in favor of James Gillray's seriously uncomplimentary straight portrait. (Really, that's not supposed to be a caricature.) Given that Turner's biography is admiring instead of critical, the US cover is...not, perhaps, what one would expect.