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.