I think that Zinn's basic argument is that the framers who constructed power through the Constitution did so to ensure that there was still an imbalance of power in the new nation. It is for this reason that the Revolution proved to be a "kind of revolution." There was change, but the change existed in who possessed power of ruling economic and social interests and not the change in the power distribution, itself. It is for this reason that I think Zinn's analysis is compelling. The revolution changed the agents who held power, but did nothing to alter the power structure that keeps individuals entrenched at the bottom at the cost of those at the top. Consider Zinn's thoughts on this point:
Beard applied this general idea to the Constitution, by studying the economic backgrounds and political ideas of the fifty-five men who gathered in Philadelphia in 1787 to draw up the Constitution. He found that a majority of them were lawyers by profession, that most of them were men of wealth, in land, slaves, manufacturing, or shipping, that half of them had money loaned out at interest, and that forty of the fifty-five held government bonds, according to the records of the Treasury Department.
In this, Zinn points out that the framers, the men who occupied power, after the Revolution had little concern with marginalized groups such as "slaves, indentured servants, women, or men without property." For these individuals, little changed and in this, Zinn develops the idea that the American Revolution was a "kind of revolution."