It may be that the features introduced by the new package are included as a patch to an existing package for older releases or, as was mentioned previously, release as a new patch which installs the new package on the older releases.
For example, and using an example from the registration component of the SUnUC toolset, the initial Solaris relase has a package called SUNWbreg but from Update 1 this was removed and replaced with SUNWbrg due to some changes in the process. The initial Sol 10 release will never have SUNWbrg installed on it is not compatible . Similarly the Update 1 and above hosts will never have the SUNWbreg package installed.
If you have concerns regarding this packages being missing I would advise you to re-post your query in the Solaris 10 forum as this forum is specifically for issues with the patching software and not the patches/packages themselves. Someone in thr Solaris 10 forum should be able to assist you better than we can.