From the NY Times website article:
QUOTE
Last week, seeking to bolster their bid, the Jets brought together six developers who agreed to pay $440 million for unused development rights over the railyard if the city would rezone the site, a process that could take at least a year. But the authority had warned against contingent bids, and yesterday Mr. Kalikow rejected the $440 million addition without discussion. Also, the Jets' previous $280 million part of the bid was discounted to $210 million, after a maintenance fund was subtracted and long-term payouts were adjusted.
So the $720 mil figure comes from the $440 mil and the $280 mil figures above. Cablevision's offer according to the article was $400 million. I think they had similar add-ons to what are listed in the Jets' offer which led to the higher reported amounts. The MTA apparently decided to consider only strict cash-up-front bids for the property.
The Times article also says:
QUOTE
The authority's chairman, Peter S. Kalikow, argued that the Jets' plan would be of greater benefit to the city, because it would assure the city's intention of extending the No. 7 subway line to the west, and would make it possible for the agency to sell development rights for the stadium property. Several members said those rights - which they said could be transferred to nearby properties to allow higher buildings - could be worth as much as $1 billion over time.
Both arguments were fairly new, and may have represented an effort by the board to justify its reasoning in preparation for a lawsuit.