Reading the reddit thread on this, it seems that the DMCA takedown was because the review is using copyrighted images/material that is authorized for use by GoPro resellers, of which digitalrev.com is not one.

I found this comment by photoknut[1] summed up the story:

"I'm sure the DMCA was used a general way for GoPro to have this article pulled. Sure they could've had lawyer contact lawyers and go through all that, but I'm sure this was easier. They clearly don't allow unauthorized resellers to use their images, that definitely falls under the umbrella of a DMCA takedown notice. GoPro owns those images and says who can use them, DigitalRev clearly can not. "

He goes on to mention that digitalrev has a shady history of re-selling the camera they damage in reviews as a new product.

1: http://www.reddit.com/r/gopro/comments/1anq5d/gopro_doesnt_l...