There is no myth out there. IMHO. It is totally possible (though unlikely as already mentioned multiple times) - for errors to happen after transferring an old tank to a new tank - which results in ammonia, etc issues. Thus, even though it's 'rare', it's prudent when one has a 200 gallon tank with 20,000+ dollars of coral, etc. to monitor chemistry for a couple days afterwards (along the lines of an ounce of prevention is worth a pound of cure). If you want to take it to extremes, in reality - those that are testing alkalinity, Ca, PO4 Nitrate more than 2-3 times/week are probably most often getting 'normal' results and are wasting their time and money. But - they know if their corals are using more alkalinity, and Ca etc. Skip cycling a large tank involves several steps - its sometimes difficult to do it as fast as one would like to - meaning its possible that things to change/die/etc. Again - most people with large tanks probably have the experience to do it without any issue. It is impossible for anyone to state with 100% certainty (IMHO) - that there will not be a problem with a given tank change, i.e. skip cycle. Thus - testing for ammonia, etc after a skip cycle in a larger system would be stupid NOT to do - given the potential risks.
I believe there are also work threads out there talking about tanks that have had problems with this method - mostly when moving old sand with the rock to the new tank.
By the way - I think I read you writing something along the lines of if you increase the bioload in a tank the bacteria on the rocks will rapidly increase and there will be no ammonia issue (if you didn't I apologize). In reality - if you markedly the bioload (lets say you have 3 tangs in a 50 gallon and you add 5 more), You may very well have an ammonia issue. Likewise - if you're doing a skip cycle - lets say a 20 gallon to a 100 gallon tank, and add only your old rock into the new tank, but multiply the bioload by 3, its entirely possible that your rock may take days to make up for the increased bioload.