@Lasereth: StarCraft and Brood War can't be played together (I mean, u can talk in channel, but that's different). These three games will have SEPARATE multiplayers (being released years apart from one another) and will NOT be able to play in the same game as each other (as of now...Blizz's production model could always change).
@Frossbyte: Incorrect, based on the understanding of the bnet forums and the mods there. Each game WILL feature all races in its multiplayer. However, each game will 'upgrade' the multiplayer, similar to the way Brood War did (just a couple new units), and thus be incompatible.
I would LOVE for the multiplayers to be compatible, btw
. I would probably only buy the Terran game in that case (and subsequently upgrade the multiplayers however Blizz did it, probably patch). This is NOT their current production model AFAIK.
@Proph: I agree that I'd love for the games to be multiplayer-compatible, but that's not as profitable a business strategy. Thus Blizzard will introduce new singleplayer and multiplayer content in each game. If you want the MP content of the protoss game, as of now you have to buy the game to get it. You can't patch ur WoL game with the new units, unfortunately :\.
What's ironic is that with the new editor, we could PROBABLY create ourselves anything Blizz does in the later games and all just chill on the Terran game
.