Opening in the same tab is the default behaviour of links in most browsers. If you want to, you can probably configure yours to always open links in new tabs, or like Tomte said, middle click on them. I don't like websites altering default behavior either, especially since it's usually so easy to open in a new tab anyway when you want to.
You could email them and suggest it. Since they don't specify a doctype in the page and browsers are using quirks mode, it should support a target [1] without issue.