Here's an interesting fact from Gabe Desjardins of Puck Prospectus:
"72% of all regulation play during the 2008-09 season was spent tied or at a one-goal differential."
This is why I think people are simply talking nonsense nearly all of the time when they start going on about goalies who make the big saves or who make saves at the key times. Most of the game is "key time", because there just aren't that many goals in NHL games. "Key" implies an important or pivotal time in the game, and it seems to me a bit improper to use that word to refer to a situation that includes nearly three-quarters of the saves a goalie might face.
Let's say we had an extreme case of a goalie who puts up a .920 save percentage in one-goal or tie games, but then completely tunes out and stops caring when the margin gets to 2 or higher (.890). If the shots against are distributed with the same 72/28 split, his overall save percentage is going to be about .912. Given what we know about how teams play to the score (shot rates tend to drop in blowouts and tend to rise in close games), that assumption is probably false, which means that there will be even less of a save percentage difference. In addition, that goalie might save a few more wins for his team in close games, but he'll also make it much harder for his team to come back occasionally from a 2 goal deficit, and he would also frequently put his team at risk of giving up 2 goal leads. As a result, I'm not sure there would be much of an increase in the team's win totals.
This shows that even an impossibly extreme split leads to an overall save percentage difference of just .008. Even if there are actually some goalies who consistently either raise their play in tight situations or lose focus a bit in blowouts, that is likely to have a very small effect over the course of an entire season. Let's say in the above example the goalie had a .910 save percentage in the blowout scenario, for a drop of .010 (which is about the difference between an average goalie and Roberto Luongo). That would leave the goalie's overall save percentage at .917, very close to the original .920.
The converse is also true, that a goalie who plays poorly during the 72% of the game that is "key time" is likely to have poor overall stats as well. It is not possible that a goalie can be so good in non-pressure situations that he makes up for having awful stats in close games. Let's change the example to a goalie who can't handle the pressure and can only stop 89% of the shots against when the score is tied or his team is within one goal. What save percentage would he need to have in all other situations to end up at the same .912 as in the first example? The answer is .970, and it obviously goes without saying that nobody is going to consistently stop pucks at that rate in any game situation.
It is not plausible to me that a goalie can make up a large statistical gap through timing his saves. Hockey is a fairly low scoring game, and as a result most of the time the score is close. Goalies who make a lot of saves also make a lot of key saves, and goalies who allegedly bear down when the game is close will spend about 3 minutes playing with extra focus and competitive fire for every 1 minute they are supposedly goofing off in a blowout. If one goalie has clearly better numbers than another goalie but a lower win total, then that is almost certainly not because of "making the key saves", but rather because of differences in the number of goals the two teams scored and the number of shots against each team allowed.
Note: Even though I've never seen much evidence to support it, I'm not ruling out differences in clutch play between goalies. I just don't think the difference would be very large and therefore we would need a huge sample size to be able to identify it. Even if we find some differences between goalies over a multi-season sample, we might still not be sure whether we are observing a difference of luck or a difference of skill. This uncertainty makes it something that is probably not really worth worrying about for the most part.