Whoever stated it is "what the Galaxy Nexus should have been" is quite correct, IMO
The differences are minimal to what the Nexus doesn't have compared to the S3. But what the Nexus HAS compared to what the S3 DOESN'T have is a little larger. You can look at what the devices shipped with and you can look at also what can be added via root.
SOFTWARE
Sooooo, when you look at software, the Nexus obviously is further ahead than the S3 due to the Nexus having 4.2.1 while the S3 is still on 4.1.2. With that also comes the largely updated 4.2 apps that the Nexus has; Camera w/ photosphere, Gallery, Gmail, Google Now, etc..... Not sure if the S3 has and can use Google Wallet or not but that's something I have actually been enjoying. I thought it would be dumb but I find it very convientent and I love the look on people's faces as if I'm a magician.
HARDWARE
Then there's hardware which the S3 DOES have an edge over the Nexus with. They both have the same Cortex A9 processor with the S3 being 200Mhz more. They both have the same amount of RAM at 1GB. They system chips differ though. The S3 has the Samsung Exynos 4 (4412) which has made news recently with the HUGE security issue while the Nexus has the TI OMAP4460. They both have SAmoled displays BUT the Nexus has 316ppi over the S3's 306ppi. Quite noticeable but maybe not to the unknowing user. They both have the same Camera with the S3 being 8mp over the Nexus's 5mp and they both record video in 1080p at 30fps.
DIFFERENCES
So, what should the Nexus have had the S3 has? Bigger camera? 200mhz more? Touchwiz..........I hear crickets at the thought of the Nexus having touchwiz. It makes me nauseous even thinking about it. The rest of Samsung's bloat? Sorry I'm reaching trying to find more that the S3 has. I can find more that the
NEXUS has that the S3
NEEDS. So I think your statement "Whoever stated it is "what the Galaxy Nexus should have been" is quite correct, IMO" should be reversed. The S3 should have been an advanced version of what the Nexus is, being that the S3 came out 7 MONTHS AFTER the Nexus.
SO, the moral of the story is the S3 came out
7 MONTHS AFTER the Nexus and had very very very similar features with the Nexus having
MORE being that it has the latest that Android has to offer. So i think it's safe to say that the S3 should have been
MORE than what it is instead of saying the the Nexus should have been what the S3 is. Kind of a far fetched statement when
EVERYTHING is laid out side by side isn't it?
This is simply a long drawn out reply to your comment with information that everyone already knows. In no way is this an argument nor am I trying to be an ass as that's not my intentions.

I just wanted to point out that the differences are very minimal hardware wise with the S3 ahead and largely different software wise with the Nexus ahead.
I love both phones as they are
BOTH ground breaking phones. The Nexus has obviously stood the test of time being a year old and is still the #1 development phone on the market today. Samsung took what the Nexus had and made it appealing to the masses. I mean look at the global sales, it's undeniable. With that being said, I am
NOT discrediting the S3 for what it is. It's obviously a great phone, I mean it's basically a steroid infused Nexus

Take away Samsung's garbage they added and you have a Nexus. Sorry, I don't care for Samsung's "skins" or their atrocious touchwiz. Gag!
I've rambled far too long. Please don't take offense to what I've said and don't get defensive. Once again,
NOT my intentions at all.
Have a Merry Christmas to you, your family and everyone else on Android Forums. My home away from home while sometimes within my home. O_0