Very simple reason....Remember when Gizmodo first released the pictures of the "found" iphone? They mentioned that it was in camouflaged to look like an Iphone 3gs...In reality it had a early bumper design. If all the engineers were testing the phone with the bumper on, they probably never experienced a lot of the signal issues that people with naked iphones are seeing today. See the attached pic of the Gizmodo "found" phone with the "camo". Since I used to do quality control for a living, I say this is bad quality testing on Apple's part. However, I do love my iphone with the bumper on!!! No signal issues here once its on.
http://gizmodo.com/5520164/this-is-apples-next-iphone
Original quote from the article:
"You are looking at Apple's next iPhone. It was found lost in a bar in Redwood City, camouflaged to look like an iPhone 3GS . We got it. We disassembled it. It's the real thing, and here are all the details."
Also Gizmodo's original picture with the "camo" on. Probably a prototype bumper
http://gizmodo.com/5520164/this-is-apples-next-iphone
Original quote from the article:
"You are looking at Apple's next iPhone. It was found lost in a bar in Redwood City, camouflaged to look like an iPhone 3GS . We got it. We disassembled it. It's the real thing, and here are all the details."
Also Gizmodo's original picture with the "camo" on. Probably a prototype bumper