From an Apple support document:

In rewriting these applications, some features from iWork ’09 were not available for the initial release. We plan to reintroduce some of these features in the next few releases and will continue to add brand new features on an ongoing basis.

It goes on to list features coming back to Pages, Numbers and Keynote. It's odd for Apple to be as open about future plans as this - but it probably speaks to the volume of comments they got wondering where things like customizing your presenter display in the new Keynote went.

There are also instructions on how to revert a document to a previous format:

  1. Documents that you haven't edited can be reverted to the iWork ’09 version by selecting File > Revert To.
  2. If you have edited the document and want to preserve the edits, you can save it as an iWork ’09 document by selecting File > Export To, then choosing Pages ’09, Numbers ’09, or Keynote ’09.

Features Coming Back to iWork for the Mac