As to comparing Starcraft to Half Life or SC to JK, I think that's silly. They're different types of games.
Sure you could say a fighting game like Mortal Kombat has a silly plot compared to an RPG like Baldur's Gate, but the purpose of the first game is action and competition, not the storyline (it's basically just filler). The second game, the RPG, is all about the storyline and character developement.
In a war game like Starcraft, the plot is just a motivation for fighting. The point of the game is just to destroy your enemies while outproducing them. JK SP is about the storyline... but MP is just about killing and competition. Half Life has its own story, but MP is just about killing/competition, etc.