Maybe you're misremembering? This is what Chief Justice Rehnquist said,
Speaking for myself, I think it does make
a difference: In a significant minority of
the cases in which I have heard oral
argument, I have left the bench feeling
differently about a case than I did when
I came on the bench. The change is seldom
a full one-hundred-and-eighty-degree swing,
and I find that it is most likely to occur
in cases involving areas of law with which
I am least familiar.
-- Rehnquist, William H.. The Supreme Court
(Kindle Locations 4154-4157).[1]
Especially as politics and the law has become more partisan (ideologically if not according to party), of course oral argument will be less likely to change the ultimate judgment. But in a caselaw system as ours reasoning is nearly as important, and sometimes more important, than the particular judgment. Just look at the way the Federal Arbitration Act jurisprudence has played out. The most recent decisions are utterly divorced from the text and history of the relevant legislation and only make sense if you track the chain of reasoning in the preceding caselaw.
[1] I found that citation elsewhere and bought the Kindle book for the actual text. The original citation I found cited to page 243 of the print edition.