Yeah, I've watched BB since since season 3, and I'm confident that they allow the HGs make their own decisions, but the producers do have far more influence\control than the audience understands. Its a bit like watching a Vegas magic show, where reality of what the audience perceives, is very different than the actual reality that goes on behind the scenes to control the audience's perception.
There have been a couple of seasons where the producers made some bad decisions and the season were a bust, and all the major HGs got evicted, leaving nothing but pawns left in the game. I think they have learned a lot since then, and like Survivor, the producers can predict with 98% accuracy that one of 4 players will be in the final 2. Their ideal is to have 2 of their key HGs in the final two, but I think that is extremely rare, generally its one of the power players vs a pawn. The last thing they want is two HGs in the final two, who stayed in the sidelines the entire time, never won a comp, and ends up in the final two simply because they were weak and lucky.
Overall, I am OK with hocus-pocus stuff they do because the show is fun to watch. I am soooo glad they cast real people from a cross section of America. They could make the show filled with stud college guys and beach babes with big boobs that have sex on the live feeds, and they all have aspirations to become models\actors. If they had gone that way with casting, I would have stopped watching.