I hope you don't mind if I steal this, osbornep.
By all means, go right ahead. Glad I could be of service. 
I'd argue Planescape is a very different beast, if only because the character you play can be defined however you want, but is still constantly faced with its past lives, that it has to deal with. I'd also point out that if PST was a sequel to a game where you played a previous life of the Nameless One that included the Save Import, the game would have been weaker for it, due to the very specific events and characters you encounter as a result of the choices made in another life. If the game had to take a "middle of the road" approach to these choices, then the setup of the game would have been much less intricate and gripping.
I'm not sure it's much of a difference, to be honest. No character is ever completely a blank slate, after all. No matter what, your PC in DA:I is going to be the head of the Inquisition, is going to have as his/her goal stopping the Veil tears, and is going to somehow be "special" with respect to accomplishing this goal. Also, I'd argue that if PS:T was a sequel at all, it'd be a weaker game. Stories about amnesia tend to be frustrating when they consist of a character trying to figure out information the audience already knows; the element of mystery is gone, and we just end up waiting to learn the same information a second time.
Eh. Okay, fine - but that still makes the decisions from DA2 rather pointless, since the romances weren't handled in a revolutionary way. Also, STORIES can revolve around "who is sleeping with who." Because the characters aren't being controlled by the audience. We can't yell at Romeo and tell him not to kill himself anymore than we can chose to have Hamlet not listen to the crazy ghost of his father. These stories are defined by their characters and their flaws. When making your own character and story through an RPG, you risk making your character mundane if you give no method of defining your character's flaws by answering difficult questions. It just so happens that some of the biggest questions to answer are also tied to big choices for others (such as picking a king or wiping out a village).
Sure, you need to be able to define your character by making difficult decisions, but precisely what I have been challenging the entire time is the idea that difficult decision = decision that will shake up the setting dramatically. This is what I was trying to get at with the Luttrell example; it's a morally complex decision which allows your PC to express your values, but it isn't going to change the course of the war all by itself. I also don't think that creating your own character means quite the same thing as creating your own story: You can have your character act as you wish, but the game is under no obligation to make the world respond as you'd like.
What on Earth makes you think the game wouldn't have to acknowledge the decision? You killed all of your companions on one choice. ME2 did that with the Suicide Mission (not on one choice, though, but through a series of them) and the developers lamented it, saying "what were we thinking?!" when they tried to create way for the sequel to be able to handle the consequences.
Unless the game gives you a group of temporary, disposable companions to kill based on one decision. In which case... what does it matter? Who cares if they are dead? You won't see them again in a future title or later in the game, since the fact that they could all be dead means every second devoted to them becomes divergent content that fewer and fewer people will see. And Bioware is not (and cannot) be devoted to making limitless amounts of divergent content, as much as I or anyone else may want them to.
What makes me think this is the fact that DA is a very different beast from ME; every DA game has a different protagonist with a mostly different group of companions (sure there's the occasional cameo from previous games, but even these aren't really necessary IMO). Your decision in the Luttrell scenario will be of critical importance to your current PC, but I don't see why it would be of great importance to your entirley different PC in a future game. I also don't see why your companions or decisions wouldn't matter at all unless they matter to future installments; isn't it enough that they matter to the game you're playing? Why does "mattering" have to be present on the grand scale or not there at all?