One of the great mysteries of the NFL news cycle is the league's formula for awarding compensatory picks in the draft. The league does not disclose the formula, but with every passing year, the best puzzle-solvers following pro football become better at cracking the code.
Philly.com published a thoroughly detailed article on what we do and don't know about the league's compensatory pick formula. They also predicted which teams would receive compensatory picks, and assigned round values for each pick as well. The Buffalo Bills were originally projected to emerge with one seventh-round pick, but have rectified a mistake and concluded that the Bills will not receive one.
If the prediction is wrong, and the Bills do net a late-round compensatory pick, it will not be because of a net player loss in free agency, but because of a net value loss from a contract perspective.
Buffalo found themselves without the services of a lot of notable names in 2013 from their 2012 team, but cut players - Ryan Fitzpatrick chief among them - do not apply to the compensatory pick formula. Therefore, as the Philly.com article points out, they lost two players (Andy Levitre to Tennessee and Chad Rinehart to San Diego) and signed two themselves (Alan Branch and Manny Lawson).
A third notable Bills free agent signing, Kevin Kolb, also does not qualify for the formula because he missed the season with an injury. The "net value" possibility comes into play because Levitre's contract far outweighed those signed by Branch and Lawson (and Rinehart, for that matter).
Again, this is just an educated guess being made by the Philly.com authors, so treat it as a rumor for now. But it's now looking like the Bills will need to maneuver around the draft board via trade if they're going to pick up extra picks in the 2014 NFL Draft.