I honestly don't really see the big deal of this, or what the problem is.
It doesn't bother me at all, but I'm one of those who does that, so there you go.
Also, I guess I can tell when someone isn't at the site anymore through the time stamp on the Who's Online page.

But anyway.. the reason it's like that is because of the cookie function of the browser. They don't like logging off/back on every time. Just like me.

I doubt it's possible to create code like that, though. But what do I know, I'm not a programmer. =P