There's nothing really new in the feature that can't be obtained through a recommendation, which gives a person additional room to expand on the reasoning for their recommendation. With endorsements, your only options are "endorse" or "skip," so other than the act itself, it doesn't really serve as a testimonial.
It's true the whole discussion could be seen as academic, since no one's going to give someone a bad recommendation, just as no one's generally going to give someone a bad reference. You will likely either give one or you won't. LinkedIn -- and its users -- would have been better served if the site had created a portfolio area or something similar where someone could actually showcase work. Let's hope a feature like this will be coming soon!