This idea is mentioned in the book as a speculation by the characters,
and Pham Nuwen says something of the sort as the Zonal surge is activated
by Countermeasure. "It was designed by something beyond the Powers.
Maybe there are Cloud People, maybe this is signalling them. Or maybe
what it's done is like an insect bite, something that will cause a much
greater reaction.... Oh, the ghost of Old One is amused. Seeing beyond
the Powers was almost worth dying for."
As far as the Zones being there to protect other races from the Powers,
I have a couple of problems with the idea. First, one suggestion is that
the primary purpose is to protect hypothetical intelligent gas clouds
in the galactic core (the "Cloud People" in Nuwen's statement above).
No explanation is given for why anyone would believe in the existence of
these intelligent clouds. Presumably no probes, automated or manned,
could penetrate to the core and return. Also, how could such clouds
exist when all other forms of intelligence, machine or organic, are
suppressed by the Unthinking Depths? (Of course this gets into the
implausibility of Zones putting a cap on intelligence or technology,
which as far as I'm concerned is just the one impossibility we have to
swallow to enjoy the story.)
If the purpose of the Zones is instead to limit the Powers to the
Transcend and leave most of the galaxy to lesser races, it seems
like overkill. Most of the interesting stuff goes on in the Beyond.
The Slow Zone, which encompasses much of the galaxy where thinking can
occur, allows only a limited standard of living to its inhabitants.
If I were setting it up, I'd let the Beyond go all the way down to
the core. The Slow Zone seems like protection enough for any gas
clouds. Unimpressive "empires" like the Qeng Ho, with their ramscoops
and generation ships, offer little enough threat. And the deep Beyond
should be relatively safe from the depradations of the Powers, while
still allowing convenient interstellar travel and communication.
Oh, well. Someday I'll have a galaxy of my own to experiment with. Then
you'll see it done right...
Hal