Pricing an ebook based on number of pages is silly. Would you pay 20% more if he added an equivalent number of pages? I think the author should charge more for a shorter book, since it respects the readers time.
That's not to say that there isn't any variation at all. This book may, in fact, be more information-dense than similar books in its category. But I was observing that publishers' prices and book length do tend to be correlated, warranted or not, and so to be competitive, it may be beneficial to price accordingly.
Edit: I just read through the sample chapter, and I didn't find it much more information-dense than other similar books. Which doesn't really surprise me, because you can only write so tersely when you're doing things like feature set walkthroughs. So I think I'm going to stand by my statement that for books of this particular type (a user guide for a piece of software), the length of the book is probably a pretty good proxy for breadth and a not-bad proxy for value.