The Blackhawks have been an interesting team this year.
First of all, there's plenty of evidence which suggests that the Blackhawks are a pretty solid team. They've accrued one of the best goal differentials in the league up to this point in the season, despite playing in the league's toughest division in the better of the two conferences. They've also soundly outshot the opposition, both at even strength and in general. In these respects, it would be difficult to argue that the Blackhawks are not one of the league's best teams.
What I find unusual, then, is that the Blackhawks expected goal differential, as calculated at hockeynumbers, is only slightly positive. The Blackhawks have allowed some 20 fewer goals than what would be predicted on the basis of shot quality, while having scored some 20 more. Given that their shot ratio is more or less in line with their goal ratio, the implication is that Chicago has been below average in both shot quality for and shot quality against. Indeed, if the expected goals numbers are translated to yield a shot quality index for each team, the Blackhawks do in fact fare quite poorly.
The fact that the Blackhawks tend to allow high quality shots against is not surprising. Firstly, shot quality is repeatable on a year-to-year basis, with Chicago having ranked 27th in the league in that regard last year.
Secondly, teams coached by Joel Quenneville tend to allow high quality shots against on average. Outside of 1999-00, for every year that Quenneville has been a head coach in the NHL, his team has ranked in the bottom half of the league in terms of save percentage, which implies that his teams were surrendering high quality shots against. While it's perhaps true that Quenneville was burdened with poorer than average goaltending during his tenure in both St. Louis and Colorado, shot quality has been directly measured from the 2002-03 season onward, with the results tending to support the argument that Quenneville-coached teams are poor in terms of shot quality against.
The Contrarian Goaltender has also found evidence that the effect of Quenneville's coaching in St.Louis was to reduce the save percentages of his own goalies, who tended to have better save percentages prior to playing under Quenneville (see, for example, the comments section of this post).
With a team save percentage of 0.912, the Blackhawks goaltending has been nothing short of superb this season. However, the fact that the team apparently allows such high quality shots against, not to mention the fact that save percentage is at least partially a product of random statistical variation, inevitably leads to the question of sustainability. Of course, It's true that both Khabibulin and Huet have proven track records, and both goaltenders are certainly better than anything Quenneville had to contend with in St. Louis and Colorado. Nonetheless, I think that it's a potential cause for concern and, at the very least, something that one ought to be mindful of in evaluating the team's prospects for the postseason.
As for the team in general, I'm inclined to think that they're still pretty good, the shot quality numbers notwithstanding. As I intimated in the above paragraph, both Huet and Khabibulin are above average netminders and the Blackhawks team save percentage is in that sense somewhat sustainable. And while it is true that the Blackhawks have exceeded their expected goals for, I'm reluctant to ascribe the difference to luck considering their plethora of offensively talented and creative players. Furthermore, even if I happen to be wrong on these points, their tendency to convincingly outshoot the other team is, if nothing else, encouraging.