I don't know the answer to your second question, Pierre.

 

I can say that much that requires programming syntax in IQ is in English in Zoot (that's good for me)

In some ways it's simpler to use, in some ways it's more complicated (I'm not used to multiple dB's for example)

Zoot makes smart folders very easy to create, in fact, much of it is automated. It's harder in IQ

The GUI  in Zoot is excellent, IQ''s leaves much to be desired.

OTOH, I think IQ is much more malleable, i.e. it can take one piece of data & illustrate it in more ways than Zoot

Zoot can sort eMail, Tweets, RSS feeds ; all of which can be very useful if one is a data fiend. I'm sure IQ could too but maybe implementing it is not as obvious to me.

Editing notes in Zoot is easier than IQ; one can easily edit HTML, RTF or text w/o worrying about an external program

IQ gives seems to offer more control over each item, adding to fields, etc. is easier in IQ than in Zoot 

Like IQ, Zoot can link items. In a way, IQ's way is simpler but Zoot can create multiple links in one command

I don't think Zoot offers equations like IQ

Zoot offers more robust clipping

Currently neither IQ nor Zoot have limitations on the size of their dB's

 

This is just a short list; I'm sure individuals who have or do use both programs & are more experienced can offer more substantial similarities & differences..

Both IQ & Zoot are very capable & creative programs IMHO

 

Bottom line, I think Zoot has more useful bells & whistles while IQ can be used in more situations.  
I have a helluva lot of respect for both you & Tom Davis & both of you have a lot of respect for your users. Both of you offer great support

 

I've been following Zoot since Ver 1

but 

I've been following IQ since BEFORE Ver 1 :-)