Is R' Elyashiv the posek hador? RHS said he thinks not. The reason is very simple. Even in the Haredi world in Israel R' Elyashiv is not accepted by all. The Hassidim listen to their rebbes, the sefardim to R' Ovadya etc. For example MK Litzman accepted a position in the government even after R' Elyashiv had said not to because the Gerrer Rebbe told him to accept it. Sefardim hold from R' Ovadya Yosef and listen to him even when R' Elyashiv (or R' Shach) disagree. In Bnei Brak, R' Nissim Karelitz is 1 of the main poskim. There recently was a dispute about who should be a Rosh Yeshiva in Ponevezh, R' Elyashiv said 1 thing and R' Nissim Karelitz and others disagreed. We see from all this that there is no 1 person whose authority is accepted by all of the religious world.
Therefore just because R' Elyashiv says something doesn't mean the YU/MO world has to listen, he is not their Rebbe/Rav. YU has poskim who can pasken any question and they are the ones who need to be asked by people in that community.
This is not to take away from the kavod or gadlus of R' Elyashiv, it is just that there is no 1 godol hador/posek hador today.