This is pretty much the best defensive lineup the Pirates could put out there and they did against Arizona. One might argue that Pedro is a better fielder than Harrison, but 3B is Harrison's best position and he accumulated 1.1 WAR in 60+ games there in 2011 (SSS, esp. re: defense, I know). Snider and Tabata might be a wash, but in the infield, this is it, and it's elite up the middle.
It doesn't amount to a hill of beans if you can't pitch or hit.
One might also say that defense isn't important until you don't have it. I'm not trying to say anyone can play shortstop, or even 1B/LF (coughAdamDunncough). Rather, I think range, or lack of it, matters less in a single-game context, especially for infielders. I get that lack of range can cause more goundballs to become hits, and hits keep innings alive, and alive innings can end up in runs. But my lying eyes (go ahead, bash me) tell me that a guy that can hit better and make routine plays, is better than a rangy guy that is an automatic out.
I'm not at all anti-sabr, and it would be great if advances in batted ball technology can tell us more about who is a good fielder and who is not. A run saved is as good as a run scored. I just doubt good defenders save that many more runs than an average defender, specifically a defender that can simply pay attention, catch, and throw. Don't ignore defense in roster construction, but put it in its proper perspective. Right now, defense carries too much weight. I'm all for the lineup above in the 9th inning of a game we lead (the lead would be 1-0 of course, maybe 2-1), but let's get that lead first, consistently.