Robertus--Americans often have bigger skimmers on their tanks than you Europeans do! Non-skimmed tanks are sometimes talked about hereâ€"Borneman has talked about his for years, but it is not that common in my experience. And while obviously they do work, and corals grow in them, I have yet to see pictures of colorful SPS corals in such a tank...? (But I suppose part of that problem is the individual defination of "good color" that each of us have).
Many aquarists here too talk about not doing very many water changes, and I'm with you-â€"how do they maintain ionic balance and the renewal of elements not commonly dosed? (because these same people that talk of infrequent water changes often talk of dosing no supplements either). For instance many aquarists have linked low potassium (K+) levels to fading and poor health in Montipora corals...
I guess in the end there are many ways to do things, and to grow corals, and to each his own. Like you I have found that a large skimmer, regular water changes, and the Zeovit system works the best for beatifully colored corals and good growth...
It sounds like you had a good and learned time at the Marine Event. How nice...!