I ask myself to what extent is the EV notion applicable to PLO, i know that mathematically the concept doesn t change , but would you apply the same NLHE EV idea to plo too?
EV is just a term used in gambling as a general. PLO, NLHE, heck tiddly-winks...a bet
will typically be +/-EV, or there are some bets that are just considered even--a coin flip.
Expected Value is just a term which can be applied to anything. 'I bet that bird A will land before bird B. I'll give you 3:1 odds.' If you see bird A is 1 foot off the ground and bird B is 100 feet off the ground, that would be a dumb bet, or -EV (the bet he is trying make with you has negative expected value/you will most likely lose the proposed bet).
EV does not say if you are playing well, or is only applicable to one game or another. EV says if a particular bet is supposed to be profitable or not.
Most of the time in poker you are working with incomplete information, so even though the bet of AA vs KK is +EV for the AA, if you hold KK, you may get the money in willingly before you know that the hand is actually -EV for this particular situation. Like Chippy said, you are betting against his 'range' of hands so KK is still a +EV starting hand.