Maybe some history will clarify this Nexus-Galaxy S debate.
Google brings out Android - way cool. Vendors (carriers and makers) bicker and whine that there's just sooooo much to do. Google says fine, we'll do a phone - enter the Nexus One, based on the Qualcomm Snapdragon and built by HTC.
While fans and pundits and other manufacturers complain about capability of the handset and whether or not Google was being fair, the Nexus One establishes a baseline hardware configuration for a fully mission-capable Android platform - able to last into the future past its intended sales cycle while able to run Android updates. It's not only Android capable - it's FULLY Android capable. This establishes a milestone in the business and gives users a chance to have a pure Google phone. It is planned from the beginning to only have a limited run - it was based on 65 nm semiconductor technology rather the latest cutting edge stuff - to prove the point that Android did not have be as adult a puzzle as others would have people believe.
Google announces their last performance update will be Froyo, Gingerbread will follow with UI enhancements, and after that, we all go to app city for improvements.
Android takes off like gangbusters. Google expands and improves Android and now Gingerbread includes performance enhancements - the end is not in sight.
Users complain while carrier/vendor combos drag their feet rolling out Froyo updates (and continue to do so, with Gingerbread already knocking on the door).
Google repeats history - time for the second Google phone to protect the pure Android brand.
HTC responds by offering to do their part at the deep discount they provided for the Nexus One. Samsung, eager to make the claims that they're the new Google phone, offers to engineer the new platform to Google specs, free of charge.
Google, not being fools, choose the Samsung handset.
If you want the Google phone, you buy one that says Nexus on the box, and go with the carrier selected by Google. Google provides the updates and gives full Android openness - the carrier and the handset maker have nothing to say about it.
Otherwise, if you want a good Android superphone (I prefer calling our class of smartphones that personally), you can select your favorite carrier and just choose the top-model Android phone that you like. Or, you might like a top-model Android phone and be ok with the carrier it accompanies.
Unlike the Google phone, however, from that point forward, your choices are to either accept what the carrier/maker gives you for software - or - you root, and wait for some developer to get whatever's working on the Google phone working on your model.
So - if you're a carrier without the Google phone - the Nexus - then the Nexus competes with what you have, like a Galaxy S.
If you're Samsung, you're already making the SoC Hummingbird processor, the display, probably the new Sammy mobile memory, etc - and you don't care what handset the incarnation is - it's all Galaxy S-based, it's all going into your pocket.
As far as missing NFC - give it time. Rumor is that new SD cards are coming with the NFC goodness inside to update handsets built without it.
There's one thing the Nexus S will compete with and that's nonsense.
Any false claim of Android non-upgradability made by a carrier or maker becomes toast if it's supported on either Nexus phone.
Hope this clarifies and helps, some.
