I do UI\UX design and coding for a living, so when I look at things like this, it flags me. For example, let's say that someone designed a car where you had to stick your finger in your ear while turning the key to start it. I could honestly say to you, "It's not that difficult to stick your finger in your ear while turning the key", and that's true enough. But... would you buy that car? I mean, why is it really necessary in the first place?
Most news aggregate web sites that I visit on a daily basis link to a new tab. This is very helpful, because I can browse down the page and click the links I'm interested in without losing the page I'm on at the time, then go read the articles, and tab back and forth to the list of news articles I was looking at. This works well and is how I "expect" it to work.
As the owner of a news aggregate web site, I want people to be "on and reading" my site. I don't want them to navigate away from my site, I want them to STAY on my site. To that end, having every single link on the page navigate away from the site makes no sense whatsoever, and requires extra care on behalf of my readers to use the site in a way that it should really work in the first place. That's inefficient and not in the best interests of HN or its readers.