Several things have been done differently during the development of Solaris 2.5. More internal users run versions of Solaris 2.5 no more than one or two weeks old. A number of large customers ran 2.5 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, instead with just 5 for OpenWindows and a number for unbundled products.
Solaris 2.5 should run most everything without requiring patches.