There are certain customs restaurants in Japan follow when serving dishes that originated overseas. Fried rice should come on an octagonal plate. Steak must be accompanied by a few wedges of carrots, steak fries, and corn.
When it comes to curry and rice, the roux should never completely cover the grain. Ideally, it should be poured over half of the plate, allowing the customer to enjoy mixing the two together in whatever ratio they feel is best.
Trying to keep with the spirit of this tradition caused problems for one Tokyo restaurant, though, when its special plate of three kinds of curry ended up containing an unfortunate and unintentional hidden image.