Ubuntu releases just as often as Fedora--twice a year. The difference is that while Ubuntu's LTS is still called Ubuntu, Red Hat's LTS is called Red Hat--and Fedora remains the semi-annual update. While Red Hat does charge for their flagship, CentOS and others do release their copy fairly shortly after RH releases.
There was a time from Fedora 8 through Fedora 12 where they were releasing almost monthly, Shadow. I switched to Ubuntu back in the 8.04 days.