JM69:
I PERSONALLY think the reason is that it allows more "mystery" and "controversy" to leave the door open to airplane problems rather than the more "boring": "well, the pilots simply forgot to flip a switch and that was enough to bring a whole ariplane down".
I hope you're correct, especially with teams of US lawyer crawling all over Spanair and MAD airport.
Why can't they just say that the slats and flaps were not "Correctly deployed" for reasons still being investigated? Perhaps the translation is difficult and this what they did actually say. Unless, of course, they know something that w don't know regarding mechanical issues?
Have Boeing issued anything more?