Some publishers find a dual orientation to be too much work, and opt for a single view. Vertical orientation is often closer to the print version of a publication, and can require less reworking, but a horizontal orientation can give more of the feel of spreads, especially for photography.
Our colleague Keith Gilbert, DPS expert and scripter extraordinaire, recently assembled a list of several DPS publications and their orientations. It’s not intended to be a scientific study, but a just quick snapshot of what decisions various publications have made regarding orientation. We thought we’d share the results with you.