Interesting...
As for a reason for the lack of berseker probes (apart from the obvious answer - lack of civs to send them), i think they're just dumb from the point of view of the specie's own survival, because they'd operate on the dangerous assumption that they posses more advanced technology then any life they might encounter.
I think it's reasonable to assume that (unlike individuals) civilisations would not act completly random, that their actions would make sense from the point of view of sociobiology (even if their motivations might not be always apparent).
Also there's the problem of identifying life if we move from our carbon-based "organic" type, to maybe other chemestries, artificial and hybrid types.

Berserker probes are a fascinating idea. My first question was, "Why would anyone bother?" But I can see them being developed as a deterrent, never intending to be used, much like nuclear weapons (hopefully.) But, of course, things have a way of going awry.

It's also hard to talk about berserker probes or make inferences as to what it means that they are absent without knowing what form they could take. In fact, the fact that life exists in its present form is not a good argument that these probes have not already swept the Milky Way. It could be that such probes were designed to eradicate a pre-existent kind of life, the only kind known to the probes' creators, and that they have indeed done that, creating a niche in which carbon-based life could arise.

I hope you realize that you left out the prelude to James P Hogan's "Code of the Lifemaker" which is also printed in "Minds, Machines and Evolution" which should have been in the list of references.

"...everybody has a bad day sometimes."

kewl article...wikipedia doesn't deserve it.

I like the idea of self replicating robots and the point of a geometric progression.

its the best way to colonize our own solar system, even.