I presume you meant bind 9.whatever, not bind 6.2?
Because each major release of RHEL will potentially use different version. Many people will stay away from a .0 and even a .1 release of an enterprise distro to allow a period of back porting to occur before upgrading to the newer versions. You certanily don't want to stay on the old code base forever, but there is a strong need to ensure that whatever ran on rhel 5.0 a few years ago will also run on rhel 5.8 etc. Not so for the next major version which has the right to add and remove features in the name of progress.