I have a 3G and 3GS sitting on my desk. I just took a sheet of paper and wrapped it horizontally around the curve, and marked it on each. Exactly the same. Then I did the same vertically. Exactly the same.
Same circumference, same dimensions. Same to the naked eye.
What capacity do you have? The aforementioned thread says only the 32GB is less tapered at the edges.
But, then again, you claim you can feel the 2 grams difference in weight, so you're clearly just making stuff up.
Frank Abagnale Jr. could detect 2.8g difference in weight to detect fakes.