So check it...the points are the thing, not the W so much. So let's say Ravenclaw scores 140 through goals but Gryffindor gets the snitch for 150. Overall, it's not that bad a loss, because that's a 10 point difference. If Ravenclaw just HAD to have those 10 points in the cup, then yeah, it's a big deal. But just being a loss? Not horrible. Plus, getting the snitch doesn't promise a win. If you're getting your ass beat by more than 150 points, and you see the snitch...do you catch it? You might just take the other team's seeker on a wild snitch chase, hoping to create pandemonium amongst the teams and crowd, which may or may not help your team catch up.

Now, your boy Viktor Krum ended a game on an L by catching the snitch once time because his team was just getting stomped out, and he didn't want the other team getting all those points.

So the snitch doesn't WIN the game, necessarily, it just ends the game.

Here's the wiki entry

Chasers score by sending the red, football-sized Quaffle through any of the three goal hoops. Each goal scored is worth ten points. After a goal is scored, the Keeper of the team scored upon throws the Quaffle back into play. Capturing the Snitch earns the Seeker's team 150 points, equivalent to 15 goals scored by Chasers. Since the game ends immediately after the Snitch is caught, the team capturing the Snitch is very likely to win the game. However, teams are ranked according to points scored, not games won. For example, at Hogwarts, the team with the most total points at the end of the year wins the Quidditch Cup. There are only two occasions in the books when the team that catches the Snitch loses: once during the Quidditch World Cup, when Viktor Krum of Bulgaria catches the Snitch, and once when Ginny Weasley replaces Harry as Seeker after he has been banned by Dolores Umbridge.

fka nope