What don't you understand?
If you print High Volume (usually art for other people) like canvas and fine art media I would lean toward the Canon. If I was an enthusiast (printing for the joy of it) or a photographer who prints mainly on glossy and satin, I would say this would favor the Z if you don't mind the higher up front cost of the profiling system.
When I say "print for pay" I mean people who are printing for others (usually artwork.) I generally don't mean people printing photography. Photography generally speaking has a lower profit margin than fine art (giclee) printing, so most people doing photo prints in high volumes are successful photographers printing their own work. Fine art printing on the other hand can be much more lucrative, with enough profit margin to make it worth doing for others.
Regarding the printers:
The Canon is faster, has 700ml ink carts that are available for about .36 cents per ML, compared to .45 cents per ml for the z3100. It prints on thicker media (1.5mm.) Another side advantage is that it loads cut sheets with ease from the front rather than the back, and you will never get an error (saving time.)
The Z will have advantages like gloss optimizer and less bronzing that photographers will like, but this wouldn't be an issue on matte papers. Also photographers (especially those just getting into printing their own work) will possibly not already have profiling equipment again favoring the Z if you didn't mind the upfront cost.
At this point I see the support issues with Canon as being WAY overblown. Sad considering IMO the Canon is the superior printer on the market at this time. I've now seen very many posts of people who have had issues that have been taken care of right away by Canon support. The positive support incidents far outweighing the negative. And this isn't even a part of the discussion when it comes to the ipf8000/9000 which, according to all I have seen, have been very reliable for the vast majority of owners. I've spoken to vendors of the ipf5000, like Jim at Shades of Paper who say they have moved very large quantities of ipf5000s and of them all he has only seen two ink cart failures which he took care of personally. He said of his many customers with roll feeds he has never heard of one go bad. ITSupplies.com had similar things to say.
Jonathan, where is this conclusion based on? I don't understand what you're saying here.