This is a whole lot of subjectivity. I'd argue that a player who reads the game well breaks up plays before the opposition can even attempt a shot, for instance. It's like when a goaltender makes a flashy save and then the commentator raves about it while neglecting the fact that it could have been a routine save if the goaltender executed his angles correctly in the first place. Like a desperation save, blocking a shot is pretty much last resort. If your defensemen consistently have the puck, consistently break up opposing rushes, consistently get pucks out of their own end, and consistently take away time, space, and passing lanes, then they're not going to have to block many shots in the first place.
And you've just uncovered why the "eye test" is sketchy at best. Here's a chart showing where on the ice teams tend to take shots from with Girardi on the ice at 5v5 since the 13-14 season.
The negative number (and red) means that Girardi is below average in suppressing shots right in front of Lundqvist. I don't know what conclusion can be drawn from this other than that a lot of players are finding their way between Girardi and Lundqvist. To compare, here is Nick Hjalmarsson's chart.
Pretty big difference there.