Who decides which singer goes home during the knockout rounds? The audience? If so then yes, your point is very good. Just "steal" two people you dont give a crap about, and put them up against your two favorites.
In the knockout round, the judge still decides who gets eliminated. These shows are not live yet, so there cannot be any audience voting. Even when the next phase begins, the audience only votes for the bottom 2, and the judge decides between them.
There definitely is strategy involved here, not only for this season, but how the judge is viewed in future seasons. Cee Lo and Christina already have built a reputation for unfairly eliminating contestants, and we saw this season that given the choice, most artists went with Blake or Adam if they were available.