dark spots on display

Have bought my first MacBook Pro in Jan 2007. Had a Problem with dark spots 3 times throughout guarantee year. The spots start small and grew over the time. Apple changed the display everytime. After the 3rd time they gave me a complete new MacBook (feb 2008). 2 month ago it started again. I noticed in 3 out of 4 cases that the spots where always at the same place and that, no matter where you push against the lid (lightly of course) the contact with the LCD display occurs on exact these spots. I'm suspecting now that the reason for this is that there are some connections or other parts in exact these places which bear against the display when the MacBook is closed and in your bag (there's always a little pressure on the lid during transport I guess).

The question is if somebody can verify my theory and if, why hasn't Apple changed something in the construction. Also, am I the only one having this problem? Couldn't find any case in any forums who had the problem so many times than me. And last but not least: is there any kind of cover or casing to avoid, if my theory is right, that this could happen again (took Apple also a year before they sold a layer for inbetween to avoid scratches on the display from track- and keypad, occuring also due to pressure while transport).

Would be nice if somebody could answer this. thnx