The folks who run Comic-Con International are explaining more about their new "one day" policy and it makes more sense now.
I know lots of folks, by the way, who deliberately attend only one day of the convention each year, often going to and fro via Amtrak train. They feel they get "enough" that way without the hassle and expense of having to book a hotel room. It is also not the dumbest thing in the world to plan a vacation in or around San Diego, staying somewhere far from the con and visiting it on one or two days. If you like zoos, the one in San Diego is a splendid way to spend a day and there are lots of other touristy-type things to do.