I have the exact same model TV you do, and When I play the XB 360 through it I get the same overscannng - I only notice it on a few games because of the game's HUD (in Marvel Ultimate Alliance it drove me crazy).
I noticed it also happens in regular DVD movies (I have an upconvert DVD player going through the HDMI port). So it's gotta be something with the TV.
My TV is still under extended warranty to I'll call Phillips and see if they can get a tech to look at it - hopefully I won't get the same response as you did from your tech.
I don't want to go in the service menu for fear of really messing up the TV.
Oh and my roomate's brother brought over his PS3 and hooked it up to my TV so I can see how it looks on my TV, and we noticed the exact same thing as your screenshot of The Playstation Store. I didn't notice it in Resistance or any of the other demos he had.. Didn't try Grand Tourismo demo.
Also, do you run your PS3 through HDMI? That's how I hooked it up on my TV, and it would not play any BluRay movies. My roomate's brother said something that the HDMI port on the TV is not HDCP compliant or something, and it won't work until Sony fixes it in a firmware upgrade..