This is possible because of the opensource community that freely participate in the development and share their respective knowledge and code, with no need to constantly reinvent the wheel.
Keeping OpenERP open is a matter of keeping a large community alive and growing!
The following document explain how you can participate for translation, bug reports or code improvement. 20120203 OpenERP Community Presentation
And remember, this is not a question of time or quantity: a simple bug report and you already help your OpenERP community!