[coolness]

This is exactly what most people in this thread are missing. The copyright holder, i.e the creator of the code is never obligated to do anything by the licence he chooses to release with. The licence applied to users of the copyright owners work.

[throwaway936482]

That's not true though. Open source licenses (as defined by the OSI) impose specific obligations upon me as creator - to distribute the source code for "no more than a reasonable reproduction cost" to users, allow users to modify it, and to redistribute it for free if it is bundled with other software, and not to discriminate against persons, groups or fields of endeavour in who can use it.

[smcphile]

No, open source licenses impose no obligations on the copyright holder for their own code. For example, if the copyright holder releases their own code under a GPL licence, no law prevents them from also releasing a modified or unmodified version under a proprietary licence. This is allowed by law, but the proprietary version doesn’t of course negate the rights already given to those who received the GPL version.

If a project has many contributors (copyright holders), they would all have to agree to a license change, so in practice something like the Linux kernel is very unlikely to ever change to a proprietary licence, but it’s theoretically possible.

The copyright holders are never bound by the terms of a user licence.