^ Actually yes. A character designed specifically for the novels has been added to the upcoming film: Serena Burns (played by Helena Carter).
Considering how often Skynet and the Resistance change the future, usually on a whim, it's easy to have all of those continuities be accurate. They're just different futures.
The M-5 computer blew up a bunch of starships because it had "issues". Hal tried to kill Dave Bowman by locking the door. Viki never thought to have one of the billion robots she controlled weld some metal plate over the access to her positronic brain before Will Smith shoved the virus into it. Eagle Eye thought a single mom was the perfect assassin when she needed to off Shia LaBoeuf. So, not the stupidest, but right up there.
^ I don't recall them ever showing her except for as a baby in Sarah's arms. However, interestingly, Jane Connor is the only version to actually defeat Skynet in the different continuities. Skynet was destroyed completely because it was weaker in her reality. Also, perhaps most important, Skynet never develops Temporal Transporter Technology.
And one of my personal favorites, the one with Robocop! http://en.wikipedia.org/wiki/RoboCop_vs._The_Terminator
Considering none of them tried to research and create a temporal displacement unit to off the leader of mankind in the past rather than create invisible drones to take the resistance out, I'd say Skynet is stupider than all those A.I's combined.