Then they've missed it. Technology doesn't ensure 100% accuracy. It just ensures far better than the current. Re: the correct fouls and throw ins you obviously need to draw the line at bigger decisions. I would say it's pretty simple: penalties, red cards, and offside. Offside really should be able to be done by a system that takes it out of the hands of humans altogether, with a hawk-eye type tennis technology as Wenger always says.
Ah, and this changes nothing about the game being played to the ref's whistle. Simply he has more advice, and the option to fix an incorrect decision he makes, just as he does now when referees use the advice of a linesman speaking into their earphone. Should he not take that option that would be on him, just as it is currently, but under such a system the referees that make more use of the help they get are undoubtedly going to end up prospering and being higher rated.