Why don't they blow it up?

Articles like this one argue that BP (or the Coast Guard) should set off a bomb somewhere underground not far from the leak in hopes of collapsing the shaft through which the oil is leaking. That same article implies that they won't do it because they'll lose all the work they've done so far, which has required a significant investment. No doubt there's been a significant investment made, but I don't think it's on the order of the $20 billion they've already agreed to pay to deal with the spill. It seems more likely that the response laid out here is accurate: they don't want to blow it up because it might end up even more complicated to try to contain.