Dałbym tak dość ogólnie.

A development editor has a different role from the acquisitions editor and the copyeditor. The acquisitions editor sponsors your book -- signs you on, proposes budget considerations for the project, often is responsible for arranging professional peer reviewing, and decides whether to invest in development. The copyeditor checks your writing style, spelling, punctuation, grammar, sentence construction, paragraphing, and other mechanics. The development editor (DE), on the other hand, analyzes your competition and reviewer feedback, works with you on your organization and content, helps create a heading system, develops a pedagogy plan, reads and comments on your manuscript, represents your project to marketing managers and production coordinators, helps manage the drafting schedule and manuscript length, and oversees the preparation of your manuscript for release to production.
http://www.sa2.info/HOW-TO/lepionka2.html