In their defense of complementarianism, several Council members in The Gospel Coalition have been known to preface their remarks with the insistence that complementarianism is not to be confused with either patriarchalism or with mere traditionalism in men/women relationships. To some observers, however, all three expressions are roughly synonymous. So why do we insist on the difference?
Everything turns on the connotations of the words involved, the mental associations conjured up by various expressions. An unrelated example may help. At the denotational level, one might suppose that a "Calvinist" is someone who stands in the theological tradition of John Calvin; at the connotational level, however, in some cultural contexts a Calvinist is thought to be a fatalist, while in still other contexts just about everyone supposes that a Calvinist is uninterested in evangelism. One may wonder if such people have ever heard of George Whitefield or Charles Haddon Spurgeon, but in any case both the ignorance of history and the abuse of terms are in some social contexts pretty strong. Because of my commitment to evangelism, I have once or twice been labeled "a Finneyite Calvinist." I am still unclear as to which of the two terms is more greatly abused.
In a similar vein, while "patriarchalism" may refer, rather neutrally, to a social order in which fathers rule, the mental associations connected with the term may be hugely variable. For some, it may conjure up order, stability, and fathers of the "Father Knows Best" variety. When one examines family breakdown in many of our communities, with fathers known rather more for their absence than for anything else, a little "patriarchalism" may have its attractions. On the other hand, for many others "patriarchalism" conjures up macho condescension toward women, self-promoting arrogance at the expense of "the little woman," and even (God help us) terrifying sexual abuse. Why would any Christian organization want to defend such grotesque distortions of what God has ordained? Similarly, "traditionalism" in male/female relationships calls to mind, for some older Americans, the stable families of the Eisenhower years (even while all sides acknowledge that the white picket fences sometimes enclosed more unseemly realities), but for many others "traditionalism" is associated with nothing more than preserving the status quo. If one associates that status quo with a refusal to overcome manifold injustice, then traditionalism itself is evil.
So John Piper and others coined the expression complementarianism. One of its virtues was its newness: it did not (yet!) have a history of wretched connotations. Denotationally it encapsulated what many of us were trying to say. The Bible does not present men and women as if they are interchangeable in every respect, save for the fact that only the woman has a uterus and can therefore produce babies. Rather, both men and women were made in the image of God and are of equal worth before him, but in God's good design they fit together in mutually complementary ways that go way beyond mere sexual mechanics. The substance of this complementarianism has to be filled out by careful and reverent study of Scripture, study that is as suspicious of agenda-driven traditionalism as it is of agenda-driven egalitarianism.
Terms rarely remain unaffected by the changing currents of ongoing robust discussion. Some neologisms stand the test of time (e.g., "Trinity"); others slither into well-deserved oblivion. In this case it is not so much a particular term that TGC wishes to defend, as the theological stance the term seeks to summarize, because we are convinced that the theological stance to which it refers is not only biblically mandated but also for our good---something to rejoice over rather than to rebel against. And we are unaware of any other word that encapsulates this position as well, while remaining relatively clear of distorting baggage.