Bruce Stone's sentence, so it seems, hasn't emphasized "average reality"
per se, but what Nabokov contrasts to it in order to express how
his curiosity and marvel at the world "outside" animates his fiction.
.Oates asserts that Nabokov (and his twin
literary companion) "excluded any referent to an available exterior
world," but I didn't read JCO's sweeping article in full,
for it was only an incidental find to Nabokov's quote.
btw, Nabokov's vision ( I'm thinking of J.C.Oates's conclusions
here) was prophetic: "When my fancies will
have been sufficiently imitated, they, too,
will enter the common domain of average reality, which will be
false, too, but within a new context which we cannot yet
guess."
Shouldn't we rather imagine that, instead of isolating an
"external world,"Nabokov was constantly erasing artificial distinctions so
that he could instil life into fiction and help his words to breathe,
interact, to take in and expel "reality" somehow? I'm
truly intrigued by Joyce C. Oates's words that it's the "mirror
and never the window...the stimulus for this art that, far from being
overwhelmed by nature, turns from it impatiently, in order to construct the
claustrophobic Ada or the difficult later poems of Stevens, in which
metaphors inhabit metaphors
..."