They are not worth more. They simply are considered as a better investment by the financial community. Nintendo's assets are worth way more then these 2 companies. Misleading and Irrevelant news in my opinion as these market caps constantly fluctuate anyways.
edit: Nevermind, Activision assets are about equal to Nintendo's assets. However, Nintendo's assets are worth more then double of EA's assets proving my point that market cap doesn't mean anything in terms of which company is "larger".
Predictions for LT console sales:
PS4: 120M
XB1: 70M
WiiU: 14M
3DS: 60M
Vita: 13M