Several things have been done differently during the development of Solaris 2.5 and later. Many internal users run versions of the Solaris release under development no more than one or two weeks old. A number of large customers runs beta releases on production systems, in exchange for virtually unlimited engineering support for those machine.
Coupled with some other development policies this has resulted in a release of very high quality that doesn't come with 36 patches on the first release CD, although there are always things found when the release is closed. Patches for older unbundled products are needed for each Solaris release.
Recent Solaris releases run most everything without requiring patches.