A good employer would invest in training and developing their employee. So, company should paid fully for the conference or training that is directly related to your job. If they don't, you should decide whether you want to work for someone that does not want to invest in you. The truth is that if they value something they will find room in the budget. Do not beg; either pay for it yourself (and consider it a personal investment) or get a new employer that actually cares about your development.

With that said, as a manager, I would carefully scrutinize the value of the conference or training. Some conference are so broad, it probably not that useful to the company. I would rather the employee pick a few conference in the beginning of the year, and work with them to narrow down to the most valuable one, and maybe come up with a plan for alternating local and out-of-town events to save on budget.

I really don't see the point in this. Do you not have faith in GPL? When a company sinks in millions of dollars and builds an entire business model around an open source project, they have economic incentive to participate in development (whether they realised it or not). With their dollars at stake, they are the best people to figure out what enhancement / fixes are needed. If they have their own "private" features/fixes", every time a new release comes out, they run into compatibility issues. Once they go down that road, it is not that far fetch to start contributing the project and have what they want be part of the main branch of development. They might also just sit around and wait for the "community" to do their work, but with money on the line, they have to start adding or making changes to the software.

Even if you don't agree with me, writing angry letters or complaining is really not going get you any where. If you really want to police this, close source your code or your project.