I think it's possible to motivate people by providing positive feedback. Suppose you work on a web app, and have 1k signups on the day you go live, and 2k on the next day. Wouldn't that increase motivitation? I surely enjoy watching the visitor stats of a new website, and feel more motivated when they are rising quickly.

Yes, you can't motivatve everybody for everything, but I do think it's possible to achieve something with positive feedback.