Okay so you put a thinner phone in an old case and expect it not to break?
You know how Moto released the extended BP7X battery that's 1800maH designed for the DROID1/2? They give you a new battery cover.
Read about the people on DroidForums who want to keep it compact and didn't put the larger battery cover and tried to bend the old one to fit? The clips for it would snap off or bend or warp or severely strain their phone. Good job. So yeah I haven't heard that about the iP4, but it's obvious if you're putting a 3GS case on it, you're doing it wrong. Curved backing vs flat backing.
Well yes that's my point. Not too hard to implement. There comes a point where thin and light are questionable. Like the iPod Touch 4G? It's so thin you can't hold well in your hand. Hell, this has been a problem since the 2G iPod Touch. They're quite thin you get a better grip by having a case on it. There's a point where going thinner will just impede on ergonomics. Same with going lighter. The 130g Nexus One is already quite light compared to the Droid or DroidX. Do we need to really go down to 115g?
Well from my personal experience, the samsung galaxy S is considered cheap because of the lighter built and the glossy finish, i have had the captivate, vibrant, and both are very solid phones, no flexing when you press the screen and the plastic is high grade.
The N1 or G2 are nice phones i'm currently using a G2, also but i rather have a plastic phone, as a drop can bend the metal and condition the phone's structural integrity. The plastic will just absorb the impact.
Again different taste for different people, i am not saying the GSG is a perfect design but is not like you having a fisher price. All HTC phones tend to be in the heavy side, i've called HTC to see how much is to fix a phone and they quote $150 for something like putting a new casing to a phone.
It is not fair calling out the SGS, i think most of the beef came from the N1 owners who had phone jealousy and started calling out on the SGS without handling the phone itself.