In 1997 it was decided that it iis far more user friendly to allow your visitors to decide how they want pages to open. By getting rid of the target attribute when they designed HTML4 they ensured that those pages that follow the standards do not disable any of the alternatives when you right click on the link to select where to open it. With a target the page maps the "open" and "open in a new window" options to the same thing.
When this was discussed in 2004 the target attribute had already been dead for 7 years. When you use target you are writing HTML3.2 (or earlier) and making your pages harder for your visitors to use.