OS risk is totally over-rated I think, but Leddy and PKS are different in kind of a perverse way. There was no way to get an OS that MTL wouldn't match - PKS was a core player and considered a future Norris trophy winner by MTL at the time (which he did win if fact, even if underserved.), so no one bothered. Leddy is that sweet spot where he might be worth so much more to the signing team than the Hawks that the Hawks might decide to take the compensation, or at least a have to match a much higher cap hit than they wanted. Unlikely, especially after the Bolland and Frolik moves, but maybe enough to scare Bowman a little after having been through the screw-job Wilson put on him in 2010.
But just speculating obviously - we'll see soon enough - but I hope I'm wrong.