Apparantly, you cant do a chown in Solaris. Here's more...
another one here
The reasoning explained sounds logical. Apparantly (as one of the article also explains), the restriction helps a user fill another user's quota by creating a huge file and chowning it to the other user. Even worse, if the other user doesnt have privs to access the dir hosting that huge file, he cant even delete that.
Looks like a safety precaution, turned into a bit of blockade for normal users... :(