Portland is already tied-up with long contracts with Roy and Aldridge, and them being contenders I doubt they'll play the free-agent game until those two contracts expire, as such paying Oden for four years is low risk as buying power of free-agent goes, and high reward potential if he returns and plays well and as trade asset when he expires. I don't see how you pass on the opportunity, unless owners are worried about paying that amount of money for an injured player, though I guess some insurance relief will be in place regardless.
So it all comes down the strategy of the team, if they plan to set themselves up short term to be players in free-agency, then certainly this might not make much sense, but I don't see them doing so, vs. long term value.