The standard isn't just 1 x 1/2, it is to put the half-inch-spaced wires on the side the rabbits will be on. That is to maximize the amount of surface area the rabbits' feet are on, spreading the weight around as much as is reasonably possible. I think the reason the other dimension is 1 inch is largely economy; half as many wires as 1/2 x 1/2 so cheaper to produce and buy. Go much further than an inch in between, and you are increasing the chances of wires getting bent, but the more material you put under there, the more there is for stuff to get hung up on. I have had rabbits that developed sore feet from being on wire; mostly Mini Rex (Rex are notorious for having thin foot padding). If half inch wire can do that to such small rabbits, I can't see any good coming from giving them even less to stand on. Even with 1/2 x 1, I have sometimes seen broken claws and broken toes. Having seen a rabbit get a foot hung in the 1 x 2 inch side of its cage and break its own back struggling, it just seems to me to be asking for trouble to put that opportunity on the floor, too.