This is very easy to explain.
Most of us can be considered reasonably experienced web surfers or computer users – and for us right-clicking is quite normal.
However, you will find quite a lot of people who do not know how to right-click, either because they are new, grew up with a very old version of Windows (or DOS), or are converted Mac users.
As a result, when they find a site they *like*, they do not want to be led away from it. So offsite links opening in a new window is the best solution.
I sort of guessed this when I was running Got2Bet. I’ve read Jakob Nielsen on usability, and for the most part he is entirely right. But he is not right on this one.
And, btw, for those who do right-click, the result is still the same – a new window.
Try sitting your father or mother in front of a computer and see what they do. When I ran an Internet cafe, there were so many things I assumed people would know – but they didn’t. They didn’t know how to type an URL in the address bar (which really surprised me). They didn’t know how to get to Hotmail or Yahoo mail, they certainly knew nothing about instant messaging, and I guarantee you it was as if the right mouse button didn’t exist.
So don’t always believe everything you see in black and white – follow your common sense first – and then put yourself in different peoples’ shoes if you can. The results may surprise you.