Did you catch the look on Giulini about Horowitz changing that note in the last movement?
And BTW, what does anyone think of the change?
I had never thought of there being anything 'wrong' with the usual version, but since I've seen this video (which BTW I saw a number of times in the past, because my dad loved it, and in fact he liked talking about this particular thing) .....since I've seen this video, the usual version sounds pale. I have trouble making the usual thing feel better even if I try very hard. And BTW I've never known, and still don't, if there's any manuscript showing the alternate version, or if there was any prior tradition of doing it that way; or if it was Horowitz's own idea.
They talk about it at 2:08 in the video and then Horowitz demonstrates what part it is. In the performance, it's at 42:01 -- he plays it in a such a low-key way that people not aware of it might not even notice. An odd thing is that where the orchestra has it (41:54), they play it the usual way -- even though it appears Giulini had been 'told' that the orchestra needed to play it the same way Horowitz would.
And maybe most interestingly, Horowitz seems unfazed when they do that. Dunno, maybe I missed something where Giulini had told him so-and-so about it and Horowitz said "whatever"....