The Astra Militarum codex has recently been moved from Hardback to Softback covers on the GW Webstore. It has been said before that GW will sell the hardback versions at release, but then eventually move codices over to softcover and small format books.
Its definitely a trend, that I think many people will like as well. Hardback books are by far my favorite, but I personally dont want every codex in that format.
The small format books are great for travel for the armies I want to play, and I hope to see more codices and supplements move to these. Otherwise the softcovers will do the job, with a small price reduction.
Here is a link to the Astra Militarum softback codex