No backwards compatability was included with RPM 4.0 with regards to building RPMs. One must use 6.2 (RPM 3.0.5) to build RPMs that can be installed on 6.2SBE2. There is no option to RPM 4.0 to build 3.0.5 'comlpiant' RPMs. This makes it very inconvenient to build RPMs that are designed for both 7.0 and 6.2.
Soon to be released rpm-4.0.1 will build version 3 packages if --nodirtokens is specified on the command line. However, since rpm-4.0.1 will be released for all Red Hat releases, there will be little need for the facility in a short period of time.
rpm-4.0.1 includes the ability to produce version3 packaging. FWIW, the problem of building a single package for both Red Hat 6.x and 7.x is much more complicated in general than just the version number of the packaging.