“Hence the problem. Who is to say that the P’sak will not change yet again in another two weeks.”
This is only a problem for someone whose actions are guided by posters on the wall, printed advertisements via a third party and second hand information about things a Rav may or may not have said. However, one who has a Rav who guides him has no such problem. The bigger problem, as I see it, (in the Litvishe world) is that very few people actually have a Rav. They learn in one place for high school, jump to someone elses beis medrash for a zman or two, go to E’Y for a year or two, go to BMG or elsewhere for a couple of years, then get married and settle into a community. So at the age of say 26, who really knows this person and can be a moreh derech? Certainly his Rav can pasken the black and white shaylos such as kosher or treif, or it is blood or it is not, or no you may not do that on shabbos or this is how to make an eruv chatzeros. Those questions that are more about hadracha can not be answered because the Rav really doesn’t know you as an individual, so, people have come to rely on cookie cutter style psakim that go up on the wall. Those who issue the “psak” are just hedging their bets and hoping to cover all bases. Even the “psak” issued in BMG that was published and reported on in Hamodia (perhaps other places, Hamodia is where I read it) reads more like general guidelines than an absolute psak.