I remember Seydor saying that in his book - I clearly need to re-read it. Perhaps I don't need to watch the theatrical cut after all
However, aside from the obvious changes that many have mentioned, there are a few things that really irk me about the Seydor cut in terms of simple aesthetics. I mentioned them over on another forum and am copying them here again.
The cockfighting scene when the flurry of feathers transitions to the shot of the guy being rounded up by Garrett on his horse [is] far better in the complete Preview version than in the shortened Special Edition.
One more interesting change is the replacement of the shot of the bucking horses when Billy walks out to the outhouse with a shot of Billy walking through some pigs. While the shot of him walking through the pigs is a nicer image, the shot of the horses ties in well with the following shot of the horses in a much calmer state immediately after Billy exits the outhouse. The horse shots bookend the outhouse sequence well and it's great how they are frantic before Billy retrieves the gun in the outhouse but then calm down once he exits as if representing the calm before the storm.
Then specifically to your points:
In the Turner Preview version, the owner of the brothel/saloon knocks a glass over and this transitions beautifully into one of the prostitutes turning the hourglass over. In the Special Edition we lose this nice transition because the Ruthie Lee scene has been added before it. Instead we get a decent audio transition from the sound of the glass being knocked over to the sound of Ruthie Lee knocking on Garrett's door, but it is not as strong as the original. I'm not commenting on whether the scene should be there or not for narrative purposes, but rather just on the unfortunate sacrifices that were made to the editing when scenes were lifted/added/re-arranged for the two non-Preview (i.e. the theatrical and 2005 Special editions).
In the Turner Preview, there is a nice audio transition from the song being sung in the outpost scene to Garrett sitting on the bank as if the lyrics to the song are in his thoughts. In the 2005 Special Edition, while there is a nice additional shot setting the scene before we focus on Garrett, the cut from the preceding scene (now the one with Billy and Alias fending off Chisum's regulators) is abrupt. We also lose a final shot in that scene that focuses on Billy's face almost as if in slow-motion. It's a great shot that adds a quiet tranquility to the end of the scene that then transitions beautifully to the scene with Garrett cooking his food on the frying pan.
Going by the mantra of dialogue basically being icing on the cake (i.e. a great film should still be pretty good even when watched in a language one doesn't understand), then [Jerry] Fielding makes a good point [that the scene speaks for itself]. However, the reference is more oblique with song lyrics than dialogue so perhaps it's easier to get away with it. Personally I found it obtrusive even when Leone included just the single word "Yesterday" in OUATIA, but I remember quite liking the inclusion of the lyrics to "Knockin' on Heaven's Door" here. I think I'll need to watch both versions back-to-back to compare. Either way, it's one helluva great scene and I'm glad no-one actually says anything!