The simple truth that critics need to understand is that sometimes you really DO have to weigh costs.
See, Scott Pilgrim was never going to rake it in at the box office. Sorry, but people keep forgetting that the main reason why 'indie' movies are such hits is mostly because they're cheap, so a mediocre performance still puts in a respectable profit. When you toss blockbuster money at it, it'll STILL have the same box office, but now the profit goes away.
And yeah, spending Avatar levels of money on a Guillermo Del Toro flick would have been a horrible, horrible idea too. Art is nice, but at the end of the day, the people who work for these companies need to eat, and losing your job because some director has a lifelong dream is not the way the world should work. What needs to happen is that the director figures out his likely audience, figures out how much he'll make at the box office from said audience, then makes a movie within that budget. Or, if he MUST make the huge blockbuster, then he figures out how to get an audience large enough to sustain those costs.
I'm not saying people shouldn't take risks. But there are risks, and then there are risks. Hoping that a movie like Thor makes a decent box office is an understandable risk. Thinking that Scott Pilgrim will pull in the same is just self-delusion.