you can do an upgrade to the next distro without reformatting. unfortunately the process isn't perfect and there are horror stories out there. i think most people either do a clean install of a newer distro or sit on a particular release and maintain it themselves. there really isn't much of a need to upgrade to a newer release as you can upgrade pretty much all software components anyway. you really only need to upgrade your kernel every now and then, update software you use if you want more functionality and patch the odd vulnerability.