Customer credos, charters and public commitments: When are they a good idea?

I'm in London this week visiting some clients, working with some Bain teams, and attending the Net Promoter Conference. During some of my meetings, a colleague pointed out that NatWest had just published a "customer charter" with 14 aspirational statements (link). Hard to tell whether it's fundamentally a marketing positioning -- their tag line is "Helpful Banking" -- or something more. It is certainly plastered all over their consumer home page today.
It seems many companies are busy publishing similar public commitments to their customers. Out of curiosity I did a quick search on Google for "customer charter" and came up with a pretty long list of links. Here are some of the first that came up. They are from all over the (English language) world. A few are almost silly, others seem quite thoughtful.
- NJIT Customer Service Credo
- The Comcast Credo
- National Library of Ireland Customer Charter
- Virgin Atlantic - Our Commitment to You
- ANZ - Corporate Responsibility
- UK Environment Agency Customer Charter (requires PDF download)
- Australian Government Centrelink Customer Charter
- Standard Chartered (India) Customer Charter
As I buzzed through these, I found myself wondering under what conditions a customer charter is a good idea. Among the more compelling rationale I have heard executives use to explain their intent in adopting a customer charter: