You can carry a game through map or ward presence. Don't let people fool you into thinking you must have a spectacular kill to death ratio to carry a game. As long as you carry a strong presence throughout the game, your teammates will benefit. Some times it's actually better to not have a spiked kill to death ratio, and spread the wealth.
EDIT: Wow! I didn't expect this to go anywhere. Thanks for everyone's input; it makes a discussion lively!