I was wondering the same thing. I can understand the rationale for going one-short - most of the clubs have gone that way this year. Four clubs have gone two short, mostly due to salary cap pressure - Port, GWS, Sydney. I think Freo did it because they had so many list positions to fill, and they just didn't see anyone worth filling them at the very end of the draft. I have no idea why Adelaide would have been considering it.
Could be we just really rate our current batch of rookies? Greenwood, Beech and Keath are all a chance to push for selection so they might just want that flexibility.