If you look at the next photo on the Steve's Digicams page, you'll see the green light ON (he's explaining the help function)...
On the digitalcamerainfo.com review it states:
"Top (6.0)
The top of the Optio S55 is pleasantly simple. At the far left, a cluster of six holes gives vent to the cameras speaker. Next to that, the camera is labeled “Optio S55,” in moderately-sized type. Almost dead center is the mode dial, containing nine settings and encircling the camera’s power button. A green, glowing indicator mark shows which mode is set. At its right and toward the front of the camera is the large shutter release. "
http://www.digitalcamerainfo.com/content/Pentax-Optio-S55-Digital-Camera-Rev...sical-Tour.htm
Ie. the green light is an 'on' indicator and helps index the mode dial.
Does it ever change when you change modes? It's always on when the cam is on, always off when the cam is off?
I'd say, that's that and not to worry about it