I have no doubt that different player choices will lead to different outcomes. That's already in the game. For example, you can choose to make Lae'zel abandon her duty to seek out her creche, and follow you on a wild goose chase through the Underdark instead of going after the one cure for tadpoles that she knows will work. You don't even have to roll for diplomacy. You can save the Tieflings or slaughter them, join forces with the goblins, etc. There are already lots of player choices that affect the story.
Giving the player lots of choices isn't an adequate replacement for good storytelling in my opinion though. I would rather that the NPCs make more of their own choices, instead of being empty automaton vehicles for endless player choices. When the characters being affected by the player's choices are 1-dimensional and lifeless, player choices, however numerous, become meaningless.
For me player choice is more important to storytelling than companions. Companion interactions can add to it, but it is the choices hat can be made during quests, and the possible outcomes, that tell the story of my character. And I think a game should be telling an interesting story even if I play it solo (with no companions). I'd rather replay VotMB again, for example, then NWN or NWN2.
Edit: Also, I don't think all companion content is in the EA yet. Initially Gale had no reaction to killing the tieflings, now there is a possibility to lose him. Same as with what happens if you don't feed him magic items.
Of course, this is not all. Even in the last patch a fairly large thing was datamined regarding the interactions of certain companions (still not available to players)
