I can see both sides of the argument here...................
For the Cowboys, they can tag Dez two consecutive seasons before they have to let him walk (to use the tag a 3rd time you have to pay the franchise QB tag regardless of position, kinda a poison pill the NFLPA put in the CBA to make sure 2 tags was the max a non-QB would ever get). So they can make Dez play the next 2 seasons under the tag and there is not a dam thing Dez can do about it. The team might be thinking that Romo has probably 2 good seasons left before he is done and once Romo is gone, we are going to suck so we don't need a $15 million a season WR for a rookie QB to throw to. I can understand that line of thinking and that might be the reluctance to give Dez a 6 or 7 year deal for over $100 million.
For Dez perspective, he is playing basically on a series of one year deals with back to back tags. Obviously no player wants to do this, just look at Spencer. He was tagged, blew out his knee, and had to sign for vet min the following season. This is obviously the nightmare scenario for a high dollar free agent playing on the tag. So the only leverage that Dez has is to withhold his playing ability from the team in an effort to force them to sign him to a long term deal. The problem I see with this is that after July, no team can sign a franchise player to a long term deal so holding out when the season starts accomplishes nothing because the team could not give Dez a long term deal at that point even if they wanted to. I am not sure that Dez and his agent realize this.
One last point..................I hate to say it, but this also could be related to the Demarco Murray situation. Dez really liked "De Mo" as he always would call him and Dez even tweeted Irvin when Murray signed with the Eagles and asked Irvin "what the hell are we doing here?". My point is that when the team makes a "business decision" and lets a very popular player walk due to money, it is hard to turn around and then ask other players to take "team friendly" deals. I am just saying that Dez is probably thinking that "business decisions" cut both ways. If they would not pay Murray after their best season in forever, then Dez might be thinking "why the hell should I take less money, I am going to get mine". Dez was pretty upset Murray left, just saying.