What a sad affair. Interviews and documentaries clearly demonstrating their relationship as partners, without a hierarchy. Then one baldly asserts his ownership rights, and the other realizes the naive trust he'd put in his colleague was vapor.
See 37signals for another such example: design studio, but oh, software is where we shine, but I need this tech fellow as full partner.
It's quite fair to say that Hoefler would not be in the position he is today without Frere-Jones, and by many accounts, and even how Hoefler presented things in the press, they were a partnership. Even before they started officially working together, Hoefler was consulting Frere-Jones on ideas, such as on Knockout - http://www.nytimes.com/2010/01/11/arts/11iht-design11.html
It's not like Hoefler's foundry was a juggernaut when Frere-Jones began contributing to his work, or even when he joined the company. They had several success stories - but so did FJ prior to that - and both of their largest successes all came when they were working together.