What a bogus image. Take the case off the iPhone 4. I own both a Droid and an iPhone4, so this has nothing to do with bias, but they are intentionally trying to make the iPhone look fatter than it is by leaving the case on it.
The case on the iPhone is necessary for it to operate properly. If the Optimus Black needed a case to function as intended, one should put a case on that too.
If I have to use the iPhone with a case, I think said case qualifies as part of the phone.
Regardless, the Optimus Black is still thinner, as it has a profile, whereas the iPhone is flat-backed.