Equating exchange of goods with capitalism is a form of myth making described by Roland Barthes. The process works as follows: an empirical phenomenon becomes a mere signifier of an ideological connotation (he cites a photograph of a Black soldier saluting the Frenc flag as the signifier of French imperialism). In theprocess, an abstract and somwhat dubious idea becomes imbued, so to speak, with manifest empirical meaning which it lacks on its own.
In the same vein, exchange of values becomes a symbol capitalism. In the process, capitalism appears to be "natural" since every society exchanges goods. Of course that old propaganda trick conceals the obvious fact that precisely because exchange of goods is unbiquitous in human history, it takes more that a simple exchange to to define an exchange as "capitalist" - such as property relations system that allows separation of production and ownership, externalization and socialization of certain transaction costs, privatization and accumulation of surplus, monopoly rights, etc. There is nothing "natural" about that institutional edifice or superstructure that makes a system of exchange "capitalist" - but the apologists of the capitalist ideology want to sell us the whole system as "natural" by selectively pointing to one single feature, nanely that it involves exchange of goods.
Economists are particularly guilty of this mythmaking. When they are not talking about formal modeling, which is a part of applied mathematics rather than empirical science - they give infantile examples of simple transactions (cf. the notorious lemonade stand) to illustrate their ideas. The infantilism ofthis kind of econo-babble is particularly visible in the NPR program the "Marketplace" - which drives me nuts.
Wojtek