Definition of Playmaker as I understand it:
A player who changes the momentum of a game with a single play that fuels a significant turnaround. I'm not sure this definition requires consistency. So while Roy maybe has given up lots of deep balls, he also makes the hit, or pick, or sack, that lifts the fortunes of the team. I give you the INT of McNabb for a TD that won the game two years ago
Romo, to this point, has had some pretty volatile performances. His debut vs the Giants is a good example. Made some crucial tunrovers, but also made some big plays with his feet, arm, scrambling etc. So yes he's volatile, but if the definition is single game changing plays or moments his scramble & long completion to Witten to set up the winning FG vs the Giants fits beautifully.
A playmaker, in my opinion, is not necessarily the foundation of your team. He's not necessarily the best player on your team. Newman, in my opinion would absolutely be a foundational player to our D. He largely takes away whoever he is covering. But he is not a playmaker because he doesn't swing the momentum by picking off a pass or causing a fumble. He rarely does that.