The primary reason is that in order to make the book's layout as elaborate and aesthetically pleasing as we'd like it to be, we simply need a bit more time. Given that this book is extremely special to us (and hopefully to our fans as well), we'd rather go all-out and add some really cool bells and whistles that would have otherwise been impossible due to time constraints.
The other reason is that we have a handful of heroes and villains that haven't been drawn since the original CAH rulebook was released in 2002 (Spydar, Sure-Shot, etc.) and we've decided that we'd like to have new, full-color treatments of those characters for such an important release. This gives us time to make that happen.
We apologize for any inconvenience this delay causes and we hope you understand why we made the call to push it back. We promise that the end results will be better for it. Thanks.