Nike's New Purpose?

Over the past several months, thoughts around the word "purpose" have been heard throughout the halls of St. John & Partners.  As I roughly see it, a positioning is what is created when you don't stand for something all that interesting, but you can't let the people who buy your products know that.  A purpose is what you have when you don't need a positioning to falsely augment any sense of a reason for existence beyond a profit motive.  For a long time our industry was pretty much just about the former... this isn't the case so much anymore.
With this conversation has come the inevitable question of whether a purpose has to be part of a brand's DNA from the beginning or if it is something that can be realized several years later.  Is Target really about design, or is that just their positioning because they can't compete with Wal-Mart on price?  Is Dove really for building self-esteem in girls and women everywhere, or is that just advertising to make people feel good about a big brand, owned by a big company, with a big carbon footprint, etc.?  Who knows?  The examples could go on. 
I think the answer is, "yes, purpose can be realized several years into a brand's existence."  The hard part for people like me to sometimes remember is that change doesn't happen over night and baby steps toward progress are at least progress.  For purpose to be fully-realized in a brand, everything must operate under that purpose's umbrella - not the least of which is a shared purpose by the brand's customers and fans.  Now the question is, how long do we wait for true purpose, or perhaps more appropriately, how do we measure progress toward purpose before we all throw our hands up in the air and say... "no matter how much progress brand X has made, everything they say and do is really just a positioning since they clearly aren't committed to their supposed purpose, X years later?"  This question seems trivial in a lot of ways now, but as people further find themselves defining themselves by purpose, it will be an increasingly important one for marketers to ask.  The world is only getting faster.

A few weeks ago at PSFK, Jeff Staple of Staple Design spoke of such an instance with Nike.  I'll be curious to see how else and how fast Nike continues to change their brand/operations/etc. to meet the needs of the apparent purpose they've found in making "green" shoes.