Please consider forcing all links to external sites to _blank as so:
<a href="http://www.externallink.html" target="_blank">external link</a>
This is one of the only forums I've ever seen that doesn't do it that way.
This site allows posters the option to have their link open in a new window, it's just not the default setting.
Some people find it irritating to have their screen cluttered up with a whole bunch of windows. While I don't agree with it (I use Chrome and tabs are my bestest friends), I do understand it.
Maybe make it so that opening in a new window is the default?