I've seen a lot more iPhone 3G's than 2G. When I had the original iPhone I felt extra cool because very few people seemed to have one
Now everywhere I go there are iPhone 3Gs. Apple stopped selling the 2G after the 3G was released so it's not like people are choosing to purchase 2G's instead of 3G's. I think you just happen to see a lot of the originals floating around. I seem them very rarely.