I think it's in the best interest of the club to keep it quiet. It's a psychological thing when another team comes into town knowing your team is banged up.
We probably don't know the truth about Kim so that everyone thinks he's still of some value.
I'm convinced to this day that Pedro tore (more than just "slighly torn" or "frayed") his rotator cuff.
Nomar is being treated with kid gloves for other reasons. First, the longer he sits out, the better the chances are he may sign for a little less (anywhere), but especially in Boston. Management also will probably say anything he wants them to say to keep him happy and atone for the offseason.
Trots injury sounds to be the most honest - and why not? The sox have nothing to lose or gain by lying about it. He's had a history of back problems (minors), and pulled his leg late last year. I think the leg was probably pulled about as badly recently as it was when he missed a month last year.
Remember Lyons was dealt for some guy(...) and wound up needing surgery right away.
I personally think Mendoza is a head case and that's why he sucks and isn't playing. I don't think he's injured, but I think head cases are more troublesome value-wise than a minor injury here or there. So the sox say it's a hip or shoulder tendenitis, but really he just doesn't have the marbles to pitch anymore - at least in Boston. Plus keeping him out of site (same with Kim) lessens the perception of how bad those two deals (2years/10million for each) really turned out.
Anyway, I think it's PR, but for the value of the franchise and nothing more.