In a recent interview with Dennis Byron of ebizq I told Dennis why LGPL sucks for vendor driven open source. The reason is quite simple: System Integrators.
If a System Integrator writes a Magnolia module that is not available elsewhere, he gains a competitive advantage not only against other SI's but also against us. Under the LGPL (of Magnolia itself) he can distribute that module to his clients without open-sourceing it. In other words, if the SI and Magnolia compete for a project, the SI can offer the module for free, while we would have to charge for it (because we need to develop it first, which presumable the SI has done in a previous project). To repeat: the SI takes our software and adds his own proprietary extension, while simultaneously taking away our business. Hence, LGPL sucks for such a scenario.
The GPL avoids that, because anybody who distributes Magnolia with custom extensions has to provide the source code of these extensions under GPL. For Magnolia International the likelyhood of an SI licensing Magnolia Enterprise Edition (EE) increases, because the EE does allow such proprietary extensions without open-sourceing them. Either way, the community wins - if the SI does provide the module, they gain that functionality, and if he licenses the EE, Magnolia International has more funds to drive the development of Magnolia forward.
Hence, GPL is the way to go.