There is no way any major corporation is going to give in to thugs like this; it would only invite more. If anything, these attacks are only strengthening positions already taken. Visa and MasterCard will just find effective ways of fighting DDoS attacks and move on.
This whole Wikileaks story really just shows the juvenile attitudes of those who can't understand that governments (and other entities) really do need some level of secrecy to operate effectively. Ironically, these are some of the same people who insist on the highest levels of personal privacy and become outraged at those who claim the benefits of "openness" and "transparency."