The media is portraying the $20 billion BP spill fund as a result of tough talk from the President. I think it was a lifeline that BP grabbed with great relish (so does the stock market, as their stock price has risen slightly in the day and a half since).
BP faces absolute bankruptcy from the torts resulting form this current spill, along with some criminal charges. Its best hope is to negotiate a deal, Chicago-style, with the US government. In exchange for a cash fund that will sound really large in the press but likely will fall short of actual claims, Congress will pass a law limiting its liability to just+ the settlement fund. The public justification will be that the settlement fund will provide much quicker and more efficient compensation to victims -- which might even be true.
If one wants a model, just look at the tobacco settlement. While they vilified them, the government in fact made tobacco companies their partners. Since the settlement, the government has in fact stepped in to protect the large tobacco companies from competition and price erosion, in large part to protect parties to the settlement from loss of market share to parties who are not on the hook to pay out large sums to the government. By the way, note that the vast majority of the tobacco settlement money did not go to its stated purpose of tobacco education and health care costs, but into the general funds to support politicians' whims.
This is how things work in the corporate state (and, I suppose, in organized crime). Once you have an entity like BP vulnerable and under your control, the last thing you want is for them to die. You want to milk them for years, both for cash and political support, the quid pro quo for being kept alive.
Update: OK, it seems I can't be original. Others are thinking this too