Whirlwind Attack hits so fast that<em>everyone</em>adjacent gets hit, while Knockback and a few of the bull rush based feats are quite capable of tossing folks around.  While the mechanics between non-magical maneuvers and feats may be different, the fundamental differences are fairly trivial.  They're both advanced combat training.  And there're supposedly techniques and forms behind any marginally disciplined and effective Fighter's fighting style.  The only difference in Nine Swords is that they mean something.  Something little more overt than many feats, much of the time.<br/><br/>(You do know you're talking about a game where a mid-level character can easily survive tap dancing on lava and be all better within a week with no lasting consequences, all without any application of magic, right?  High-level D&D characters are undeniably far beyond the ken of ordinary mortals.  3e's just wishy-washy on the matter.  When you hit high levels, you're not talking guard captain Bob anymore.  You're talking<em>Gatts</em>.)