The argument of the poster (which i think in most of the case is correct) is that it is usually the DA which make the agreement, and can advise the judge on it, but the judge seem in no way forced to respect the agreement.
I believe that's an accurate summary of US law.
From the Swiss point of view, however, this raises the issue of whether that's a good (fair, just) situation or not. If the judge is not obligated to respect the bargain struck by the DA,.... well, see my earlier post about "welshing on a deal."
The defense lawyer contentious point in this case is that the judge *himself* seem to have made a step toward and backward (your welshing), while at the same time some poster say "it did not happen that way".
... and since the defence makes that point, it must be addressed somehow, even if only to be dismissed out of hand. The Swiss opted not to dismiss it out of hand and requested further information, which was refused. Small wonder the extradition failed.
This isn't really that unusual. As Darat points out, the UK makes a point of not extraditing people who might face the death penalty. The "usual" procedure in such case is for the United States (or whoever) to give a firm undertaking that the defendant will not be sentenced to death. It's never been clear to me on what basis the Department of State has the authority to make such an undertaking, or what would happen if a jury in Alabama decided "sod it all, we're sentencing this thug to death" in the teeth of such an agreement.
But one of the things that would happen is it would suddenly become a lot more difficult for the US to get extraditions in death penalty cases, since the USA would have proven itself to be an untrustworthy bastard.
That's basically the situation here, as I see it. The Swiss want to know what will happen to Polanski, just as Her Majesty's Government might want to know what would happen to one of HMG's prisoners. The US has refused to give any undertakings,.... and in fact, has refused to provide documents that the Swiss consider relevant to determine whether someone is breaking an implicit, if not legally binding, bargain.
In light of that refusal, I don't see any possible grounds for complaint by the Americans.