That has bothered me as well, since they have never been clear about it. What they have said is that you can get to the optimal ending with or without MP. What was asked of them and from my understanding never answered was what differences will it make in the SP experience. You know will I have a different experience in any way if I don't play the MP. What cut-scenes and dialogs are going to be different? That to me is the big issue. I am very much a completetionist and I get the feeling I will not be able to be like that with this game without having to play the MP.But more bothersome to me is the link between MP and SP. In spite of all the assurances from BioWare that you can get a complete game experience from just SP, I think SP and MP are more tangled up than they admit. This is based on several posts on this Galactic Readiness in MP and how it affects SP and about the point system they use in game to calculate Galactic Readiness, etc.
Bitching aside I am still looking forward to the SP experience.