Hay un poco de historia en la wikipedia:
http://en.wikipedia.org/wiki/.tkSegun la wikipedia, son dominios gratuitos con el proposito de generar ingresos de las visitas de los dominios .tk
El dominio está administrado por la compañía de comunicación del país Teletok y BV Dot TK, una compañía privada, cuya razón social es proporcionarle ingresos a la población del archipiélago mediante la venta de estos dominios. Constituye una exportación o ingreso no convencional del archipiélago de Tokelau, que es mayoritariamente un pueblo de pescadores con algo de producción de artesanías.
Los dominios de .tk pueden ser gratuitos o de paga. Las restriciones de las cuentas gratuitas:
No legal ownership - the ownership of a free .TK domain name remains with the registry.
Registration restrictions - registration periods for .TK domain names are restricted to 1 to 12 months
Renewal required - the renewal for the free domain is required (at no extra charge) for a free domain is required and is available within 15 days prior to the expiry. Failure to renew that free domain can lead to termination of service: the domain is cancelled by registry
No transfers allowed - you cannot transfer the domain unless you upgrade it to the paid version.
Minimum use requirement - you must have a minimum of 25 unique visitors within the first 90 days after registration, or else the domain is cancelled by the registry.
A free .TK domain name can only be forwarded to an existing URL, or pointed at existing nameservers.
A paid domain name means that the above restrictions no longer apply; you become the owner of the domain name, and as such you can manage it as you would any other domain name.