Chase, I know you are looking for Will's opinion but since you posted it here... :)  I would agree that all movement should have purpose but I don't think only using a reaction based strategy will work either.  It may for a touch or two but a better fencer will pick up on it and exploit it.  I think movement with purpose applies equally to being defensive as it does offensive.  Use movement to either counter act your opponents movement as you have described above or setup your offensive action or counter action.  Whenever we fence I often talking about exploiting gaps that people leave.  To me this means exploiting the point in time where distance meets timing.  Whether that comes after a movement on my opponents part or during the movement itself is another part of the phrase.

As for the quotes directly, I would think it would translate well to staying balanced.  If you are centered (balanced, or rooted) at all times movement in any direction flows naturally and effortlessly.  Being rooted mentally also applies.  Dictates of offensive or defensive action can flow freely in any given situation or part of a fencing phrase when you are "looking" at nothing while noticing everything.

I am likley well off the mark but it was an interesting post that got me thinking a bit...just my 2 cents from reading what you wrote.  Interesting post, thanks.

JS