The paid plugin system is being designed to allow 3rd party developers a way to be compensated for their work. Some paid plugins will be released by the HB team (which I assume some will be free for lifetime members) but others will be released by 3rd party developers.
Most 3rd party developers will not receive any "cut" of the money that you paid for HB Lifetime. Therefore, they will have the option of making their plugins paid so they can collect money for their work. If you don't want to pay for it, you will have to deal without the plugin. It will be the developer's choice to release plugins for free, or to make them paid.
Also, the HB team is probably still working on the business model to support all this so please don't bitch and moan about it until you see an official announcement.