If you're ONLY going to Worldcon to attend the convention, don't plan to do anything else at the destination, and don't mind having all your meals at the convention venue, that's a valid argument. If you'd actually like to do anything else while you are there, the weather is more of a consideration. I gather that Orlando weather isn't always as horrible as when I was there for Magicon in 1992, and that Disney basically air-conditions the entirety of Disney World, but all else being equal I'd rather go somewhere that has weather that is actually pleasant at the time of year I would be visiting.