This is not a case of theory v. practice, but of defining terms. The term corporation (referring to a business entity) and corporatist (referring to a way of organizing society) are linguistically related but mean different things.

Here's a cut and dry political definition of corporatism from answers.com . . . .

And from that article, here's a bit about the corporatist idea:

"Although the modern debate started in the mid-1970s, the idea of corporatism has a long history. Guilds or corporations were important institutions in mediaeval life, but attracted little attention from political theorists. Conscious reflection about the potential prescriptive value of corporatist arrangements really started in the last quarter of the nineteenth century. In the papal encyclical Rerum Novarum (1891), Leo XIII tackled the problems of the poverty of the working classes, the development of trade unions, and the prevalent 'spirit of revolutionary change'. It was argued that class conflict was not inevitable, but that capital and labour were mutually dependent. Noting the general growth of associative action, Leo XIII argued that problems such as working conditions and health and safety could be dealt with by specially established organizations or boards, with the state sanctioning and protecting such arrangements. The object of proceeding in this way was 'in order to supersede undue interference on the part of the State'. This concern with limiting direct state intervention, and finding alternative forms of state-sanctioned associative action, has remained a central theme of the corporatist debate. The association between corporatism and Catholic social theory has also remained a strong one."

I hope it is clear that I am NOT defending Italian Fascism, or even advocating for corporatism per se, but rather pointing out that Mussolini's term "corporate state" is often misunderstood.