1. Well Marchand is 34 and is going to miss a few months to injury. Missing your top point-getter from last year is no doubt going to hurt, and missing him for that long and hoping at his age that he can rebound quickly and get in mid-season form by December is optimistic.
2. Then, you're missing your #1 defense for a few months as well. Ask Montreal how it felt to lose their #1 defense last year. I know it won't be for a full season, but losing a #1D is a massive blow, and your right side on defense looks incredibly shallow without him.
3. Finally, you look at your top two centers: 37 years old and 36 years old, one of whom didn't even play in the league last season. They're fantastic players, but they are older and I don't think it's unreasonable to expect a decline from either of them, if not both of them.
..I don't think Boston is in a playoff spot by American Thanksgiving, so can they be an exception? Personally, with the age of their top 6 centers and injuries to key players, I don't think they will be an exception to that rule, and won't be able to catch the rest of the pack.
Of course I could easily be wrong, this is just a prediction and just for fun, so don't let it bother you too much.