How does trading down work? How did DW know that his guy (Goldobin) would still be there at 27? Is it kind of an 'insult' to be selected with a pick that was lower than your team's original pick? Or was the point really to acquire the 62nd pick as well?
I think it's a combination of both of the above. Odds are, DW had a couple people he was good with at 20 and he expected they all wouldn't go between 20 and 27. By most lists Goldobin (ISS Ranking of No. 28) was expected to go around 27 so it's a risk DW considered to be worth it to move up the 6th rounder to an early 3rd (a pretty significant jump). If you can do this, and still end up with the person you would have picked at 20th, then it was worth it. The Blackhawks made the opposite move, and probably didn't think that Nick Schmaltz would be available at 27th (ISS Ranking of No. 24)
Btw, here's a nifty value chart for draft picks that gives some idea of the value between various draft picks in a pick-for-pick trade.
http://myslu.stlawu.edu/~msch/sports/Schuckers_NHL_Draft.pdf
I believe we received 467 value points vs. giving up 418 value points. So, not counting for which players were actually chosen, we "win" that trade. I think it's typical for the team trading down to "win" because those trading up are more likely to overpay in order to make the deal happen since they're the most interested in ensuring the trade happens to pick "their guy".