From the article I read, Surtain for a second round pick was what the Dolphins were looking for. The Chiefs had thought they could get him for a second round pick, but after Buchanon of the Raiders was dealt to the Texans for a 2nd and 3rd rounder, the Chiefs had to up their offer. A 2nd round draft pick in the NFL is valuable; you can get very quality players (e.g., Surtain). In comparison to the only other prominent draft, it is hit and miss (much more miss) when drafting a player in the second round of the NBA.
The Dolphins also would have had to sign Surtain to a long-term deal, and in the time being, he was eating up their cap space at a charge of 8.3 million for this season.
Look at two of the most successful teams in the NFL over the last several years. Two years ago when the Eagles lost Bobby 'the blanket' Taylor and Troy Vincent, I thought their secondary would suffer, but they had two young guys come in and solidify themselves as good starting cornerbacks.
When the Patriots lost Poole and Law to injury last year, they had a couple talented players come in and contribute to another Super Bowl title. Thus, Law has been expendable, where areas last off-season he got away with calling Belichick a liar and still stayed with the team.
Here is the article I mentioned
http://sports.espn.go.com/nfl/column...len&id=2043410