Nah, it's very easy to be objective when on a 5 pages homework, one write 5, and the others 0. Or if only one person has compiling code on their machine the day before the project. Of if only one person speak on the conf because the others don't have anything to say.

I've never personally seen that. I've seen cases where one person writes four pages, and one writes one page claiming it was the hardest. I've seen cases where one person writes the code, and one writes the paper about the code. The only case I've seen where one person does all the work the person who does all the work refuses to allow the others to help.