I don't agree. These seem fine to me. With these things, if I were pledging $50 it would mainly because I liked the project and wanted to support it. The fact that credits and thanks are actually free, is kind-of irrelevant. Their percieved value is much greater. I'd say that $10 is actually a little low for a DVD. Based on your estimation of $5 per DVD, what if the OP got their $4000 from 400 people all donating $10? They'd need to spend half their budget on DVD's and they'd need to specify that their budget for the film was actually $2000. Realistically, buying in bulk, I think a DVD might cost between $1-$2, but it still need to be accounted for.
jbueno192... I too do not like flexible funding campaigns, for the reasons specified above. If you changed that, I'd certainly consider donating.