KAV update hourly = we get fastest protection against Zoo/unknown virus?!?

Not really a few hundred.
According to the report from F-Secure, it is 3255 in total (May, 2005).

It depends on what you mean by Zoo malware.
Anyway, the test samples are chosen using VS2000 according to many AV programs. To qualify as a valid virus sample, at least 1 anti-virus can detect it, not something which is found only in virus labs.

 

It is usual since the are techies.
Techies like jargons.
In Economics, when they are talking about "goods", "capital", "land", "enterpreneur", "cost"; don't expect they mean the same as or similar to daily usage. Rather the opposite is the truth.

Even within experts, they may have different definitions on ITW and Zoo too.

Anyway, forget these confusing tech labels.
ITW is more to do with spreading, existing, known viruses.
Zoo is more to do with non-spreading, potential, new viruses.