Have a feeling the Spikes era is not going to come to a pretty conclusion
Total speculation but given that Spikes' contract expires after this year, it's possible this is related to a desire for an extension OR said desire already being rebuffed by the team. Other members of his draft class have notably been extended (Gronk/Hernandez) and others (Cunningham) won't be offered the chance to return. Spikes isn't an essential piece for the future (I'm not a fan of his skill set in this era, while acknowledging he'd probably be a Pro Bowler if this were 1985) and should be on the field less in 2013 than he was in 2012, if the Pats pass defense is going to improve.
IOW, it's about money. leverage and playing time. As long as he shows up when it's mandatory, it'll be OK.