You don't need to for most open-source software. You are free to take any GPLv2 software, modify it and host it on your own servers and charge a usage fee, all

You don't need to for most open-source software. You are free to take any GPLv2 software, modify it and host it on your own servers and charge a usage fee, all without publicly releasing your changes - it's an unforeseen catch in certain open-source licenses that only requires source release if the customer can get their hands on the binaries - if it's accessed through a browser or over the network then they lose that privilege.