It works better though, if you start from zero and hire people that drank the Koolaid.

It's hard to shoehorn it into an existing team where some portion of the team doesn't believe the premise. For example, some people (introverts, Asperger's spectrum, etc) will just never be comfortable with pairing.

Pivotal doesn't have this problem because developers that don't believe wouldn't ever apply for a job there.

But, that doesn't help Pivotal in their consulting practice. Very few of their clients would have the same advantage.