This is extortion.
No, it isn't. Extortion is defined as the use of force or threat to achieve a gain of some sort for the party threatening the use of force (i.e., I put a gun to your head and say "I won't shoot you if you give me $100, otherwise I will").
It also isn't blackmail unless Wikileaks is attempting to achieve some sort of gain for themselves by threatening to release the information publicly unless these companies fail to pay them.
In other words, if wikileaks isn't gaining anything (money etc) from this, it isn't extortion or blackmail. It's Wikileaks allowing the tech companies to fix the holes the CIA created before they release information about those holes to the general public - thereby possibly allowing the tech companies to save face. That makes sense, since it's quite possible that it's no fault of any of these companies that the CIA decided to completely trash their products in the name of spying on everyone. The damage is already done, in other words, and there's really nothing stopping Wikileaks from just telling the world what the damage is. It's kind of nice of them to give Microsoft etc some breathing room first, so that when they do release details on the damage done, they can also include information that shows these tech companies have already fixed the problems.