OK, first the obvious:

David's last name is spelled "Gilmour" not "Gilmore".

That is obviously Roger Waters who makes the intro before "Us and Them". In the post-Barrett Floyd, Roger was the band spokesman and de facto 'leader' (until his departure, of course.)

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Here's where things get strange: this recording is obviously an (incomplete, seems like this source would fit perfectly on a 79:57 min. cdr) audience tape of this famous gig. Also sounds like it is in mono as well. There is a complete audience recording of this show that has been around in various forms for a long time. The WV source may in fact come from this very same tape. (Can't compare with my copy as my cassette deck is dead!)

 

Why Wolfgang's Vault would list an audience recording as "soundboard" is beyond me.

(These things must be obvious to others out there, right?)

That's a phenomenal question near the end, so I will try to answer it for you:

1. The audience recording you mentioned was done by a famous bootlegger who was known for his excellent/clear recordings of various performers (Zeppelin, Yes, the Stones, the Who, etc.). Many of these recordings were often clear enough that some people thought that they were actually soundboards, with the occasional chatter in-between songs being from the performers or people at the sound desk, and not the fans; this is sounds like one of those shows right here. Various websites note that this show is often accidentally labled a soundboard instead of an excellent audience recording, for there was little chatter by audience members, and what they do say is often figured to be performers who are a few feet from the mic(s) on stage. However, some of the recordings on WV were previously unavailable in pro-recorded form, so this could be what no one had been able to hear before now. 

2. Now having at one time listened to that recording (a couple months back), I am 99% sure this is the same source, but the fact this version is in low-quality MP3, and not lossless like WAV, is the only thing that stops me for giving my 100%, for it could really be the performers far off mic, and the low quality may sacrifice most of what makes the show actually sound like a soundboard.

3. Now yes, The "Animals" set and the encores do exist on the audience source, but are not here, similar to how the 4-27-69 Led Zeppelin show is available on soundboard for both the first and second sets, but only the first set is available here. Hopefully, WV will be given (in the best quality) the full source that floats online on many websites, so if this is an audience recording, they can post the whole thing, while if this is really a mediocre soundboard, they can bridge it all toghether for out enjoyment.

4. Lastly, it could be Gilmour who made the comment about "UAT", for having not listened to that part before now, and the recording cut down to 128 MP3, it could be harder to tell who says what.

I hope this answers your questions about the show, but remember, I do not know everything, and many people will tell you the same (Hopefully they still don't want me dead)

Ref the voice before UAT, I've just had a listen (or three) and it is VERY hard to tell who it is.

It's the classic sort of thing Roger would say and it was around this time he was getting very annoyed with noisy audiences. I don't think Dave would bother trying to shut them up, Roger would. I also thought it was Rick, which is possible as it's a keyboard intro but I'll stick with Roger as I can hear a reflection in his voice which is classic Rog. My money's on Rog.

I've been to 17 Floyd shows (19 if you count Roger tours)  - 7 of that particular tour, including both nights at Oakland, and Roger was constantly trying to get the audience to shut up.

One of the four in New York MSG someone threw a firework on the stage and he stopped the music and said (paraphrased) "You STUPID MotherF*cker.  Why don't you F*K off and let the rest of us get on with it?"

it is, without question, roger waters who is speaking at the beginning of 'us and them.'