By suggesting an increase of the number of Passives, I think you are referring to the number of people that FEEL this way. I certainly agree.
However the point of this diagram is to show how many people will go the next step and TALK about it. I believe that unless actively solicited, most people will not tell others about something they either don’t care or have a neutral opinion about.

Regarding the ratio of detractors to promoters, I think an overarching generalization would be unfair since the topics and feelings behind them really depend on the subject at hand, demographics, and psychographics.

Consumers are far more likely to be suspicious of and discount recommendations and far more likely to act on negative information even if they feel it may not be even be accurate. Most people are afraid of being taken and may avoid businesses that have strong positive recommendations if they have any strongly negative reviews or warnings online.

Because of this, businesses need to be very proactive at making sure they provide excellent service and products and in reaching out to dissatisfied customers and doing their best to resolve complaints.

Every business gets complaints and some people can not be pleased; however, the more a business listens and cares about their buyers the more likely word-of-mouth-marketing will benefit them rather than hurt them.

If you ever create a similar diagram I would make the ratio of passives much higher. The number of detractors IS generally much higher than promoters because most people are more motivated to complain when unhappy than to recommend when they are satisfied.

Because of this I am amazed that more companies are not wooing their cheerleaders. There are only a small number of people who proactively and consistently recommend anything and they can only recommend a couple handfuls of specific products or services on a regular basis. Sharp businesses should be actively seeking out and working with those who genuinely believe in them.