[madcaptenor]

(For reference, the first sentence is "This book is intended for use in English courses in which the practice of composition is combined with the study of literature.")

Out of curiosity I googled "we intend this book" and people do seem to use that wording sometimes in introducing their books. Why don't Strunk and White do that?

[jcranmer]

Not certain as to why, but one plausible explanation is an opinion that using first person pronouns would be inappropriate, as it is "too conversational" or something like that.

[madcaptenor]

That seems plausible, and pretty much demands the passive voice. Otherwise they would have had to do something like "The authors intend this book..." which is rather strange when the authors are also the ones who wrote the sentence.