I do believe the Genius Bar can replace screens. However, I don't believe that it will fix this problem. It's the internal support for the screen that's causing the problem.
I have this problem on a brand new iPhone 3GS (less than 24 hours of ownership). It was the first thing I noticed when I pulled it out of the box, and is very annoying. It scratches my ear when I'm on the phone, and is quite uncomfortable.
It's worth noting for others reading this thread that this is my second iPhone, which is the replacement for the first iPhone, that had exactly the same problem (hence the need to replace it). The folks at the Apple store said "they could open 10 boxes, and they all could have this problem," however they weren't going to open 10 boxes for me because they apparently can't open them before they are sold.
For a $299 subsidized, or a $699 no contract phone, I expect the device to be manufactured correctly, and am very disappointed. I'm considering an all-out return of the device, and cancellation of the contract, but it's unclear what all of the options are. Does anyone know what else can be done?