TWA, in response to that thread, note that the deal was 89 firm conversions and the rest were options. The _planned_ aircraft are being converted. The real story is that not all of those airframes were salvageable, the cost was more than made sense. Not too surprising, really.
As for the SR MD-11s, the price negotiated at the time of the original contract was a lot higher than the current "book" value. The company doesn't want to pay a premium for airplanes in this market, and who should blame them? They could get out of the contract for free, so they took that option. No doubt that they will get the airframes from somewhere, one way or another. Could end up being those same airplanes, just not at the same price, but time will tell. They weren't supposed to come for a while yet, anyway.