No not everyone does this. Do you have proof that people have asked planted questions.
I asked President Bush a question when he was down 15 pts last election. It was his first Q&A before the real season began and nobody approached me or noticed anyone else being approached by the campaign. I was doing phonecalls at the time so I would be a great plant.
I seriously doubt it happens on other campaigns. If you have absolute proof fine, lets hear it.
Pray for W and Our Victorious Troops
The main point that I want to make is this. When elected officials speak to groups of people, those groups of people are generally checked out--That is why many meet and greets and speeches have tickets. You might not have been able to ask the president a question if you weren’t a republican. Maybe you could have. Every camp is different, but every staff wants their candidate to look their best, and bad questions and even worse answers are a fast way to stall (or end) any campaign. You try to avoid that at all costs. Just look at some of the biggest campaign screw ups- a lot of them were caused by a question the candidate could not or would not answer.