Weeeeell, the people out in the districts -- at least, the ones on the fringes, like 11 and 12, not the ones raising Careers -- certainly don't see this as fun and games. They know what it is: it's a message. It's "We own you. We can make your children fight each other to the death for our amusement and there's nothing you can do about it."
That scene at the end you're talking about isn't in the first book (and neither is the [spoiler]riot[/spoiler]) -- I assume it's lifted from one of the later ones, though I've only read the first. But yeah, what IS clear in the book is the power of stories. Katniss manages to subvert the message, to tell a story that disrupts and undermines the story that the Capitol's been telling.
And what the movie establishes but the book REALLY hammers home is just how slow Katniss is at understanding precisely what she's doing. Haymitch and Cinna get it, but they spend most of the story trying to hammer it into her head. (I don't think Peeta is really setting out to make the audience fall for them, either; I think he's just being earnest. But he DOES seem pretty savvy at the whole manipulation thing once they enter the Arena, so maybe he's doing both.)
And in the end, she even manages to pull off plausible deniability -- [spoiler]she could have looked President Snow in the eye and said "Fuck you," and she'd have been publicly executed and the people would have been cowed. But she kept up the act that she's a lovesick girl who didn't even realize she'd found a way to beat the system, and so they had to let her live.[/spoiler]
It's not clear in the book just how much of the decision to play Peeta and Katniss up as starcrossed lovers is Crane's decision, but yeah he's clearly the one calling the shots in the movie. And [spoiler]he bites off more than he can chew -- in his pursuit of a good story to captivate the audience, he opens the door for a better one. Yes, his "rule change" is what sets up Katniss's ultimate act of rebellion, but it's not even completely necessary -- she could have pulled the same stunt even without it.[/spoiler]