The way I see it, Belichick places on trait above all others in his QBs: consistently making the right reads. I know that sounds pretty obvious, but there's always a tradeoff, and there are a lot of teams in the league that will sacrifice a bit in that dept. to get a QB who is faster, throws harder, is more accurate, or whatever else. It's easy to say that you value everything, but, on a scouting level, you can't. Every QB has deficiencies, including Brady, who doesn't throw well at all on the move. You can still be a very good QB without reading defenses well- hell, Favre, a first-ballot HOFer, didn't even know what a nickelback was until years into his pro career, and still didn't get why the distinction mattered once he learned it.
I think you saw a lot of that in the Cutler trade this year, too. McDaniels learned from Belichick, and he learned that, whatever else Orton may lack, he's a guy who's going to make the right read. Conversely, whatever Cutler may bring to the table, he's going to make some terrible reads that will lead to costly mistakes and will make it very difficult for you to confidently wage and win a battle for field position. Whatever a big play from a QB can gain you, negative plays hurt you more than big ones help you. And really, what it comes down to is: whatever your physical gifts make you capable of, that only matters if you know what to do with them. If you're not making the right play, then you're not making the right play.
So, re: Romo, I just think he'd be a bad ideological fit for the Patriots. Do I think he'd do well if he played for the Pats? Probably- I can't imagine how anyone with his talent wouldn't do well throwing to Moss and Welker. But it's a moot point, because he's the type of QB that Belichick avoids. Certainly doesn't make him a bad player, and teams have won with QBs like him before; he's just a poor fit.
