I don't think it's quite fair to classify Jeff Green as a "backup SF". He's probably going to be a part-time PF this season, and looking further ahead, may be our starting SF of the future once Pierce moves on.
Doc made a big deal about how he had to throw away his lineup with JG at the 4, once the heart condition was found. JG didn't wow anyone playing PF in OKC, but he also wasn't playing next to KG, either. I personally want to see what Doc can do with JG this year.
We also don't know if all four years are guaranteed, do we?
And finally, gotta agree with the notion that we can't assume that other teams weren't interested in JG just because we didn't hear any rumors.