bilzzard set speed cap beacuse of there Object colllison /Order moveing fuctins in the engin is not ment to move at a very high speed . If they let you set any speed your unit could walk any where or worse the game could crash. Im shure that the felt that the blade masters windwalk max speed 522 was not givening the engin any troubble so they up it for all units. its very possable that the game is stable up 1000 or so but i doubt blizzard will up the speed agin.
Actually, technically the 522 limit isn't supposed to be 522. It was meant to be much higher, but the engine is what limits it, it's hard to explain but they didn't *set* the limit to 522, it's just kind of what their algorithms came up with. I'm sure they could rewrite it to have a large number, but it is because of the pathing/collision they have in there.