V6.1 has the same license than v7 or v8: agpl. The AGPL requires that you distribute the source code of modules you develop on openerp to users. So, you can not have private modules. We think it's fair to ask the community to contribute back since we distribute the whole software for free. That's why we choose the agpl license. With Odoo enterprise, our official maintenance contract, we provide an other license for our customers that do not want to redistribute their own module. The idea of this "private use" clause is not to show settling proprietary version of openerp/Odoo (no redistribution) but to allow customers to not share their own modules, that are key to their own business.