Not that I put much faith in the cycle type products... but it is not possible they act as some kind of bacterial steroid? The bacteria will start developing one way or another - I have had a tank which I only placed some decor and plants in and without adding ammonia or fish I went through a cycle (getting ammonia and nitrite readings)
So in my opinion, no matter what you do, you are going to go through a cycle? So with this in mind is it not possible these products simply provide some kind of boost to the bacteria developing in yourt filter, rather tahn magically making bacteria appear?
Lets take my recent moving of tanks as an example too... moved all fish from 70 and 120 litre tanks to one larger tank. Only moved filter media from 120 to the new tank, and also added some new fish pretty much immediately (perhaps not hte best idea). Also all new fresh water . So effectively, there would not be enough bacteria present to cope with the number of fish now in the tank. Surely I should have gone though a mini-cycle while the bacteria caught up?
Perhaps the capfuls of cycle I added when I moved all the fish helped with this?