Reason 1: SB Champs are 11-0 in Wk 1 this century
You have to go back to the last century, the '98 Denver Broncos, to find a SuperBowl Champion who lost their Week 1 game the following season. There are a number of things that would factor into this:
_these are obviously good teams to start with
_they are playing at home
_they are playing with a crowd able to celebrate the SB together at home for the first time
_they are playing with the carry-over confidence of being SB champs
Reason 2: Cowboys O-Line has not taken a single snap together against another team
Not one. We all know O-Line effectiveness is all about how you work as a unit. There is only so much you can learn in practice. This line will face a significant learning curve in game-time and the D-Line they are facing in Wk1 isn't going to be making things easy. This line (and therefore Romo and Murray) will take its lumps in the first few weeks.
Reason 3: Our CB's are unsettled
Jenkins has not played a snap in preason and his shoulder is yet to be cleared. Claiborne is a #6 pick but he missed half of preseason and training camp - and most rookie corners struggle in the first year - including players like Revis and Peterson. Carr looks like he is worth every penny, but the Giants have more than 1 good WR.
Reason 4: Witten will be out or less than 100%
Romo will be playing behind an unsettled line without his #1 safety blanket. 'Nuff said.
Reason 5: Our top 2 WR's have barely played in preseason
Granted, these guys have had a few seasons to build their rapport with Romo. However, they have had very limited time to knock the rust off this season. There is a much higher liklihood of a miscommunication or different read wihout that polish. This is compounded by the fact that Witten is missing.
Now, before you drag me to the stake and burn me as a heretic, I would point out that all these reasons are temporary. Many teams have lost in week 1 and gone on to win the Superbowl - the NY Giants a case in point - three times!!
The NFL these days its all about how you finish the season, not how you start. The Giants and Packers being Exhibit A and B. If there is one thing I want to see in the Garrett era, its a strong finish to the season.