I think it's a mixture of that, the similar reason that if the url shortener bubble pops, tinyurl or bit.ly could go under, and the branding. n.pr, especially i

I think it's a mixture of that, the similar reason that if the url shortener bubble pops, tinyurl or bit.ly could go under, and the branding. n.pr, especially if you've ever seen it before, lets people know it points to NPR's site even though it's shortened. Same with 4sq.com, post.ly, etc. One of the big disadvantages of url shorteners is that you have no idea whether it's the story tweet claims it is or child porn.