It seems to me that the discussion of the lowest common denominator is confusing three distinct realities. The first reality is the deepest desires of our hearts, for truth, beauty, justice, goodness, love, etc. These desires are shared by humanity, though the search for truth, beauty, goodness, justice, and love is often misguided. The second, distinct reality is our instinctual desires. These are also shared by all of humanity, but are our base desires or carnal instincts. Much of popular culture is an appeal to our desire for sex. Lastly, our appeal to a common denominator often manifests itself in an appeal to external circumstances, such as the weather or popular culture.
It is important to distinguish these three ways of relating to other people because it affects how we react to them. Oprah seems to be appealing to the deepest desires of our hearts and proposing that many different ways of getting to God may make one happy/fulfilled. The Christian proposal is that this isn't true, that God Incarnate is the only being or thing that can fulfill those desires. If people recognize the deepest desires of their hearts, then we are able to make this proposal to them.
Normally, however, people do not recognize their desires, or, if they do, they are not able to distinguish between their deepest desires and their instinctual desires. If we are aware of this difference, then we are able to educate ourselves and others to discover the difference between our elementary desires and our instinctual desires. Then we are able to better follow our elementary desires, which, if the Christian proposal is correct, will lead us to Christ.
When we talk with people about common experience, even if that experience is of pop culture, we are able to help educate them (and ourselves) to our desires. If someone likes fashion, we penetrate and ask why. What is it about fashion that's appealing? Well, it is beauty. Overtime, our elementary desires come out.
Educating ourselves and others to the desires of our hearts is the method proposed by Luigi Giussani, the founder of Communion and Liberation. It is, in the (post?)modern world that prizes the individual and the individual's desires, a very accessible method because the starting point is the individual and the individual's desires. This method begins with Giussani's books The Religious Sense and continues with At the Origin of the Christian Claim and Why the Church?