Outside Japan if 3DS struggles hard (both hardware and especially software wise) PS Vita will bomb hard, if 3DS under-performs then PS Vita will disappoint badly. The more 3DS sells the better for PS Vita since it will have more chances to be a success. This is not about consoles wars but portable console gaming ecosystem that it is apparently in a real bad shape. Mainly due to the western media and developers that hate portable consoles, they just can't conceive anything outside smartphone games.