Blizzard is calling them "expansions".
Everyone else seems to be calling them "ripoffs", though. Not sure where those folks were when Dawn of War with its incredibly uninspired single-player campaign and a million expansions rolled out. Or Half-Life 2, which already has two expansions, and a third is in the works.

Well, Dawn of War added new factions with each expansion, each of the former having a distinct play style. (Or so I'm told).
I think HoMM3/4 expansions makes for a better likening.

So if it's going to be three really long games....I dunno if I want to play as Terran for an entire games worth, you know?
Maybe they just don't know what there going to do with the other storylines lol

The last I heard is that each story will be about as long as the whole first game (wether that was with or without Brood War, I do not remember).

Well, in all honesty they say that they're taking this approach in order to make great campaigns mission wise. If we look back at the original game the missions were kind of short and the story lacking at points.