Apple only releases betas to developers so they can begin enhancing their apps for the new version of iOS.
While they do allow developers to submit bug reports, that is not the main objective of releasing betas. Apple issues much more frequent internal betas that are used to work through all of the issues during development. The last beta we received was probably already several weeks old at the time it was released to developers. Even the new beta pushed to carriers is likely several weeks old. Apple's internal testing is much further ahead, and will be ready for GM release in a few weeks time.