I don't think Leddy's trade was entirely based on contract situations. While certainly part of it, I also think he was just bad enough in the last postseason to give the Hawks some doubts about his future.
If you take Leddy's current 2.7 million cap hit and add in Oduya's number of 3.375 (who is, basically, the player the Hawks kept in favor of Oduya), that adds up to a sligthly higher annual cap hit than what Leddy will get starting next year. Now, that likely means two big contracts are gone this summer. Would you have shipped off Bickell and Sharp to keep Leddy? While this is all with the benefit of hindsight I'd say yes. You could have your entire top four D-men locked down for the next 3-4 years at under $20 million. That's pretty damn good.