Such reasoning misses one of the major points of the Worldcon, and the analogy I'm about it make is why I put the Olympic logo on this post. The modern Olympic games are hugely expensive and inefficient. You have cities spending billions of dollars for facilities that will be used for their primary purpose only once for a two-week period. If efficiency were your only goal, you would set up a single Olympic site (well, two of them actually; one for Winter and one for Summer) and hold the games there every four years. The traditional site is of course Greece, but I would suggest that Sydney would probably work better for the modern games, based on the success of the Sydney Games a few years ago.
By now, those of you allergic to sports will have already gone away. But for the rest of you, I think I hear some of you saying, "But then it wouldn't be the [modern] Olympics!" That's right. And a Worldcon that doesn't travel to a new city every year isn't a Worldcon, either.
It may well be that the people who think Worldcon should be in the same place every year subconsciously assume that the one place would be convenient for them to attend, and who, if that one place were somewhere else far away, would then say, "Well, I'd never go to Worldcon because it's much too far away. Maybe if they moved it around a bit so it was near me sometimes, I might go."
Baring some lunatic billionaire deciding to throw money away, you're never going to have a Worldcon-sized event that moves around regularly and is also inexpensive to run. The goals are mutually exclusive.