Fedora Infinity: A Dumb Question?

[kwhiskerz]

I have always wondered why it is necessary to issue a new version of Fedora 
(or any other OS every 6 months). Why cannot an OS be like a river, constantly 
flowing and always being the latest edition, with a simple yum update. Cannot 
programs clean up after themselves, leaving no cruft, so that this would be 
possible? That way, one could jump on the infinite Fedora flow at any time and 
always have the latest version of all programs. What forces the necessity to 
stop a particular version and recreate all the software and redo all of the 
old mistakes that were already fixed and issue a new version?