Nick Piecoro of the Arizona Republic explains that the Diamondbacks' Randy Johnson vs. Jon Garland decision was not as clear-cut as many (myself included) made it out to be.
Piecoro walks through Arizona's timeline. At one point in November, they expected to receive (and budgeted for) first-round picks as compensation for Adam Dunn, Orlando Hudson, and Juan Cruz. They wisely changed their minds on Dunn on December 1st, and the Hudson/Cruz market has developed slowly. Along the way, several million dollars were added to the team's starting pitcher budget.
Still, Piecoro guesses that the Diamondbacks preferred Garland to Johnson and didn't want Johnson back that badly.