I registered here just so I could also speak to this issue.
I just got the GS3 in France (I9300) and I was shocked to see that every phone I've had going back to the HTC Fuze had spot metering that worked. Granted, HTC cameras have always been best, but this is a basic function. SPOT metering both in pro photography and in any other kind means your light meter takes a reading of the number of lumens in a spot and adjusts exposure for that spot. This isn't an interpretation thing, it isn't an opinion thing, it is optics and lighting. And if it's not functioning, clearly something is wrong.
I just have a hard time believing Samsung would release something THAT broken. And yes, that does mean "broken". So what I think is that the Camera app may be at fault. Perhaps we'll all have to find a ROM that suits this function or a new camera app that does it. I can confirm that the Vanilla camera app didn't use this properly either. Would love to see what happens on an HTC ROM.
Do we really not have a solution for this? Has anyone played with other Camera Apps in the market?