The light goes out when the battery is fully charged. The battery drains slower than the plug charges. Therefore yes. If kept plugged in, your battery will never be less than fully charged. Thats why the orange light doesn't always stay on. The plug is charging faster than you can drain it, thus no need fo the orange light to stay on after the battery recharges.
No offense but if you know that the battery charges faster than it drains, then this question is really just common sense..
(edit-off topic) I really need to shrink my siggy. It stretches the boards now. :/ I can't though since I'm using my Wii and my PSU on my comp died on me >_