a) Roh Moo-hyun and his predecessor Kim Dae-jung and cohorts have created, in the Sunshine Policy, an atmosphere in which South Korea expects to reconcile with North Korea through dialogue Advances are touted by astute politicians while setbacks are studiously ignored.
b) As the Marmot points out, likely next president Lee Myeong-bak will be politically bound to go through with the joint plans made by Roh and Kim Jong-il. To not do so would be seen as unacceptable provocation.
c) As much of the joint projects will be funded by private industry (hat tip to the Marmot again), Korea's corporations will have a vested interest in both the international perception that North Korea is making progress and the continued cooperation of the Kim regime.
d) With both politicians and corporations in South Korea heavily invested in the perception of progress on the North-South issue, advances both real and imagined will be touted more vigourously while setbacks will be swept so far under the linoleum that it'll take the ondol extra long to heat up.
e) As for North Korea, they now recognize that pointing missiles at Seoul and threatening to turn the city into a lake of fire is no longer a viable means of extorting aid. It is both cheaper and easier to demilitarize while allowing the placement of South Korea's public and private sector's cherished symbols of peninsular unity to be built, at South Korean expense, in North Korea. Now, all North Korea needs to put South Korea in appeasement mode is close a plant or, in a kind of reverse Gazprom maneuver, close the South Korea-China train line. A master stroke, I must say.