Disclaimer: I am one of the founders of NeoOffice.
Being based on OOo 1.x, IBM does not need to release the source code for Symphony. OOo was originally dual licensed both under LGPL and the SISSL license. SISSL allows companies to make completely closed source forks, only providing notice of the original vendor and SISSL license. This license was one of the primary motivating factors for why we forked and created NeoOffice, to prevent companies from making a commercial product whose improvements couldn't be shared back with all the volunteers that had worked to create it.
Closed source forking is also our reason for using full GPL since it guarantees everyone's freedom to access the code. Not even LGPL provides that ability since commercial closed source proprietary code can still be incorporated provided it's in a shared library. Only the full GPL provides enough protections to ensure that everyone must cooperate and that no one can make key parts of the project rely on closed source solutions.