This paper presents the results of a genre analysis of two web-based collaborative authoring environments, Wikipedia and Everything2, both of which are intended as repositories of encyclopedic knowledge and are open to contributions from the public. Using corpus linguistic methods and factor analysis of word counts for features of formality and informality, we show that the greater the degree of post-production editorial control afforded by the system, the more formal and standardized the language of the collaboratively-authored documents becomes, analogous to that found in traditional print encyclopedias. Paradoxically, users who faithfully appropriate such systems create homogeneous entries, at odds with the goal of open-access authoring environments to create diverse content. The findings shed light on how users, acting through mechanisms provided by the system, can shape (or not) features of content in particular ways. We conclude by identifying sub-genres of web-based collaborative authoring environments based on their technical affordances.